VITAMINS
Introduction:
Vitamins are all organic compounds which, as originally defined, cannot be synthesized in the
human body and must be provided in the diet. They are essential for the normal processes of
metabolism, including growth and maintenance of health. It is known that the body is able to
produce part or even all of its requirements for some of the vitamins, Example: Vitamin D from
cholesterol and niacin from Tryptophan.
WATER SOLUBLE VITAMINS
Include the B- Vitamins and Vitamin C. They share few common properties besides their
solubility characteristics. Since they are water soluble excess can be excreted through urine.
Hyper-vitaminosis may not cause toxicity. Most of these vitamins act as coenzymes.
The B- Vitamins are essential and must be provided through diet: these include:
- Thiamine (Vit B1)
- Riboflavin (Vit B2 )
- Niacin (Nicotinic acid (or Nicotinamide)
- Pantothenic acid (Vit B5)
- Vitamin B6 (Pyrodoxine,pyridoxal,& Pyridoxamine)
- Biotin
- Vitamin B12 (Cobalamin)
THIAMINE
Thiamine is Vitamin B1. Addition of a pyrophosphate to thiamine (from ATP) converts it to
thiamine pyrophosphate, a molecule that is the coenzyme for all decarboxylations of -keto
acids.
Thiamine pyrophosphate
Mechanism of action - TPP contains two heterocyclic rings, a substituted pyrimidine and a
thiazole. The latter is the reactive moiety - specifically, the rather acidic carbon between the
sulfur and the nitrogen. This carbon forms a carbanion, which in turn, can attack the carbonyl
carbon of -keto acids, such as pyruvate, This compound undergoes nonoxidative
decarboxylation, with the thiazole ring acting as an electron sink, in forming a resonance-
stabilized ene-amine. Protonation gives a species called active acetaldehyde, or hydroxyethyl-
TPP.
Thus, in general terms, TPP functions in the generation of an activated aldehyde species, which
may or may not undergo oxidation as it is transferred to an acceptor.
Some enzymes that use TPP include pyruvate decarboxylase, pyruvate dehydrogenase,
branched chain α-keto acid dehydrogenase, α-keto glutarate dehydrogenase, transketolase.
Sources:
The good sources of Thamine are: Seeds, Nuts, Wheat, Legumenious plants (rich source) &
lean meat.
RDA: Minimum requirement 1.0mg for adults, infants and children 0.4-1.3mg
Requirment increases in conditions of Anoxia-shock, Hemorrhage, injury, illness, fever and
hyperthyroidism. Also increased carbohydrate in take, pregnancy and lactation.
Deficiency: Causes Beri-beri and related deficiency syndromes.
Mainly caused by carbohydrate rich diets. In such individuals TPP dependent reactions are
prevented, leading to accumulation of substrates like Pyruvate, Pentose sugars
Symptoms: There are two types Dry beri-beri not associated with edema and wet beri-beri
with edema, probably due to congestive cardiac failure and low plasma albumin. Symptoms
include Peripheral Neuropathy, Exhaustion and Anorexia. The signs may progress to edema
and Cardiovascular disorders, Neurological & muscular degeneration.
Wernicke Korsakoff syndrome which is frequently found in Alcoholics is associated with Thiamin
deficiency.
Diagnostic parameters: Erythrocyte transketolase activity decreases.
Thiamine excretion in Urine and Blood thiamine concentration decreases.
RIBOFLAVIN(VIT-B2)
Riboflavin, also known as vitamin B2, is a component of the flavin coenzymes, FAD and FMN.
It is composed of an isoalloxazine ring system linked to ribitol. The ability of the ring system of
riboflavin to exist as a semiquinone allows the flavin coenzymes to accept electrons either
singly or in pairs. NAD+
and NADP+
can only accept electrons in pairs.
It is mainly used in the energy metabolism of Sugars and Lipids. The activation of FMN and
FAD is an ATP-dependent.
Source: Meats, Nuts, Legumes, Milk, fish, egg etc.
RDA: 1.5-2.5mg for adults, infants 0.6mg, children 1.0-1.8mg
Deficiency: Lack of riboflavin in the diet causes a generally non fatal syndrome of inflammation
of the corner of mouth (angular stomatitis), painful glossitis of tongue (Purple) and Scaly
dermatitis.
A degree of photophobia may be due to its light sensitivity, because Riboflavin is colored,
fluorescent and decompose in visible light but heat stable.
Erythrocyte enzyme activity measurements (Glutathione reductase) is used to determine
Nutritional status of Riboflavin.
Niacin
Nicotinamide Nicotinic Acid
Niacin is not a vitamin in a strictest sense of the word, since it can be synthesized from
Tryptophan. However, conversion of Tryptophan to Niacin is relatively inefficient (60 mg of
Tryptophan is required to produce 1mg of Niacin) and occurs only after all the body
requirements for Tryptophan is met. Thus most people require dietary sources of both
Tryptophan and Niacin.
Niacin contains a substituted Pyridine ring and when gets activated forms NAD+ and its
phosphorylated derivative is NADP+
.which are co enzymes of many dehydrogenases.
Source: Milk, Lean meat, Unrefined grains, cereals and from Metabolism of Tryptophan.
RDA: Adults 17-21mg, infants 6mg.The requirement increases with increased intake of calories,
illness, severe injury ,infection ,burns, high corn (maize) diet, pregnancy and lactation.
Deficiency: Deficiency leads to Pellagra, a disease involving GIT and CNS.
The disease is characterized by intense irritation and inflammation of the mucous membranes of
the mouth and other parts of the GIT, leading to gastro- intestinal hemorrhage, Dermatitis,
Dementia & Diarrehea. (the “3-D’s” cardinal features). Skin lesiondevelop when exposed to
sunlight, become redend, thickened and becomes scaly. The patient develops gingivitis and
stomatitis (Tongue gets swollen) General effects of deficiency are Failure of growth, loss of
weight and anemia.
Vit B6 (Pyridoxine)
Pyridoxine Pyridoxal Pyridoxamine
Exists in three forms: Pyridoxine, Pyrodoxal & pyridoxamine and their corresponding
phosphates.
Pyridoxal phosphate (PLP)
Pyridoxal Phosphate
Pyridoxal phosphate participates in transaminations, decarboxylations, racemizations, and
numerous modifications of amino acid side chains. All pyridoxal phosphate-requiring enzymes
act via the formation of a Schiff base between the amino acid and coenzyme. A cation (a metal
or a proton) is essential to bridge the phenolate ion of the coenzyme and the imino nitrogen of
the amino acid. This bridging maintains the planarity of the structure, which is essential for
catalysis. The most important catalytic feature of the coenzyme is the electrophilic nitrogen of
the pyridine ring, which acts as an electron sink, drawing electrons away from the amino acid
and stabilizing a carbanion intermediate.It is also used for the synthesis of Neurotransmitter,
Serotonin and Nor-Adrenalin. Used as a component of Sphingolipids necessary for myelin
formation and Heme synthesis as well. Hypochromic microcytic anemia since PLP is requiredfor Heme synthesis.Deficiency in infants cause convelsions due to inactive glutamate
decarboxylase, GABA not formed there by impaired neurotransmission.
It is an essential component of Glycogen phosphorylase;it is covalently linked to a lysine residue
and stabilizes the enzyme.The conversion of Tryptophan to NAD also requires this co-factor.
Sources: Wheat, corn, egg yolk, Liver and muscle meat
RDA: 1.4-2.2mg for Adults, children 0.3-0.4mg.Patients with anti-tubercular treatment needs
more Vitamin B6.
Deficiency: usually is not common, but may result due to intake of drugs like Isoniazid and
contraceptives. Alcoholics also suffer from such deficiency. Isoniazid binds to pyridoxine and
makes it unavailable as a vitamin, causing peripheral neuropathy. oral contraceptives stimulate
the synthesis of the enzyme which require this vitamin, thus causing deficiency .
Biotin
Biotin Is a vitamin and a coenzyme commonly associated with enzymes performing
carboxylation reactions. Biotin is typically linked covalently to carboxylase enzymes through the
-amino nitrogen of lysine. Some of the enzymes that need Biotin for their activity include:
Acetyl-CoA carboxylase is the primary regulatory enzyme in fatty acid biosynthesis mediating
the following reactions:
Acetyl-CoA + ATP + HCO3
-
<=> Malonyl-CoA + ADP + Pi + H+
Pyruvate carboxylase is an enzyme of gluconeogenesis. It catalyzes formation of a carboxyl
group on pyruvate (using CO2) to make oxaloacetate.
Pyruvate + HCO3
-
+ ATP <=> Oxaloacetate + ADP + Pi + H+
Source: Normally synthesized by intestinal bacteria.
Found in all foods particularly: Liver, egg, peanuts & milkRDA: 100-200μg/day. Requirement increase in pregnancy and lactation. Patients on oral
antibiotics for a long period of time require more of this vitamin.
Deficiency:
Rare, since it is found in almost all food stuffs. But large consumption of raw egg white may lead
to deficiency of Biotin. Avidin, a glycoprotein in egg white binds tightly to biotin and makes it
unavailable for the necessary carboxylation reactions.
The symptoms in this case are: Dermatitis, Glossitis, Muscle pain, depression, alopecia (Loss of
hair), Loss of appetite and Nausea.
Vit B12 (Cobalamin).
The metal cobalt in vitamin B12 is coordinated with a tetrapyrrole ring system, called a corrin
ring, which is simiilar to the porphyrin ring of heme compounds. The cyanide attached to the
cobalt in the structure is an artifact of the isolation and is replaced by water or a hyrdoxyl group
in cells. The presence of cobalt and amide nitrogens gives B12 compounds the name
cobamides or cobalamins. Only two reactions occur to a significant extent in mammalian
metabolism: the synthesis of methionine from homocysteine. B12- requiring reactions involve either (1) methyl group transfer or (2) adenosylcobalamin-
dependent isomerizations. The isomerizations exchange a carbon-bound hydrogen with another
carbon-bound functional group.
Pernicious anemia arises from a B12 deficiency. Gastric tissue secretes a glycoprotein called
intrinsic factor, which complexes with ingested B12 in the digestive tract and promotes its
absorption through the small intestine into the blood stream. Pernicious anemia results from
insufficient secretion of intrinsic factor. Outlines a probable explanation for why failure to absorb
B12 leads to the deficiency of red blood cells that define anemias.
1. When B12 levels are low, flux through the methionine synthase reaction decreases but,
because adequate dietary methionine is usually available, protein metabolism is not
immediately disturbed.
2. Reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate continues
because this reaction is virtually irreversible.
3. Because methionine synthase is the only mammalian enzyme known to act on 5-
methyltetrahydrofolate, the decreased intracellular activity of this enzyme causes 5-
methyltetrahydrofolate to accumulate, at the expense of depleted pools of the other
tetrahydrofolate coenzymes. Thus, even though total folate levels may seem ample, there is
a functional folate deficiency, with insufficient levels of the formyl and methylene derivatives
needed for synthesis of nucleic acid precursors.
The action of B12 and folic acid, are interrelated. Deficiency of both produce similar signs and
symptoms and Anemias.
Source: Synthesized by Microorganisms
B12- requiring reactions involve either (1) methyl group transfer or (2) adenosylcobalamin-
dependent isomerizations. The isomerizations exchange a carbon-bound hydrogen with another
carbon-bound functional group.
Pernicious anemia arises from a B12 deficiency. Gastric tissue secretes a glycoprotein called
intrinsic factor, which complexes with ingested B12 in the digestive tract and promotes its
absorption through the small intestine into the blood stream. Pernicious anemia results from
insufficient secretion of intrinsic factor. Outlines a probable explanation for why failure to absorb
B12 leads to the deficiency of red blood cells that define anemias.
1. When B12 levels are low, flux through the methionine synthase reaction decreases but,
because adequate dietary methionine is usually available, protein metabolism is not
immediately disturbed.
2. Reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate continues
because this reaction is virtually irreversible.
3. Because methionine synthase is the only mammalian enzyme known to act on 5-
methyltetrahydrofolate, the decreased intracellular activity of this enzyme causes 5-
methyltetrahydrofolate to accumulate, at the expense of depleted pools of the other
tetrahydrofolate coenzymes. Thus, even though total folate levels may seem ample, there is
a functional folate deficiency, with insufficient levels of the formyl and methylene derivatives
needed for synthesis of nucleic acid precursors.
The action of B12 and folic acid, are interrelated. Deficiency of both produce similar signs and
symptoms and Anemias.
Source: Synthesized by Microorganisms
RDA: 3mg/day.
Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives. Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives. Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives.
Pantothenic Acid (Vit B 5) Coenzyme A.
Pantothenic acid is a vitamin that forms an essential part of the acyl-carrier moiety, coenzyme
A.
Coenzyme A (A for acyl) participates in the activation of acyl groups in general, including the
acetyl group derived from pyruvate. The coenzyme is derived metabolically from ATP, the
vitamin pantothenic acid, and -mercaptoethylamine. A free thiol on the last moiety is the
functionally significant part of the coenzyme molecule; the rest of the molecule provides enzyme
binding sites. In acylated derivatives, such as acetyl-coenzyme A, the acyl group is linked to
the thiol group to form an energy-rich thioester. The acylated forms of coenzyme A will be
designated here as acyl-CoA, and the unacylated form as CoA-SH.
The energy-rich nature of thioesters, as compared with ordinary esters, is related primarily to
resonance stabilization. Most esters can resonate between two forms. Stabilization involves Pi-
electron overlap, giving partial double-bond character to the C-O link. In thioesters, the larger
atomic size of S (as compared with O) reduces the Pi-electron overlap between C and S, so that
the C-S structure does not contribute significantly to resonance stabilization. Thus, the thioester
is destabilized relative to an ester, so that its G of hydrolysis is increased.
The lack of double-bond character in the C-S bond of acyl-CoAs makes this bond weaker than
the corresponding C-O bond in ordinary esters, in turn making the thioalkoxide ion (R-S-) agood leaving group in nucleophilic displacement reactions. Thus, the acyl group is readily
transferred to other metabolites, as occurs, in fact, in the first reaction of the citric acid cycle.
Some of the common metabolic reactions involving Coenzyme A are shown below.
1. Pyruvate + NAD+
+ CoA-SH <=> Acetyl-CoA + NADH + CO2 (catalyzed by Pyruvate
Dehydrogenase).
2. Acyl-CoA + Carnitine <=> Acyl-Carnitine + CoA-SH (catalyzed by Carnitine
Acyltransferase I)
Sources: Eggs, Liver, Animal tissue, Whole grain cereals, Yeast and Legumes
RDA: 4-7mg/day
Deficiency: rare due to its wide distribution
The burning foot syndrome in prisoners which is associated with reduced capacity for
acetylation is ascribed to pantothenic acid deficiency.
Vit C (Ascorbic Acid)
Vitamin C is a water-soluble vitamin. Collagen is unusual in its widespread modification of
proline to hydroxyproline and lysine to hydroxylysine. Most of the hydrogen bonds between
chains in the triple helix are from amide protons to carbonyl oxygens, but the OH groups of
hydroxyproline also seem to participate in stabilizing the structure. Hydroxylysine residues in
collagen serve to form attachment sites for polysaccharides.
The hydroxylation reactions in collagen involve vitamin C. A symptom of extreme vitamin C
deficiency, called scurvy, is the weakening of collagen fibers caused by the failure to
hydroxylate proline and lysine.
In general hydroxylation reactions require Vit C.
Example: Hydroxylation of cholesterol.
Functions:
• Collagen biosynthesis
• Degradation of Tyrosine
• Absorption of Iron
• Steroidogenesis
• Adrenaline synthesis
• Bile acid formation
• Degradation of tyrosine
• Bone mineral metabolism
• Potent anti oxidant
WBC’s are rich in vit C and plays an important role in Immunity.
Source: Citrus fruits, Potato, tomato & green vegetables
RDA: 60mg/day
Deficiency: scurvy symptoms are spongy gums and bleeding of gums due to defective collagen
synthesis.
Introduction:
Vitamins are all organic compounds which, as originally defined, cannot be synthesized in the
human body and must be provided in the diet. They are essential for the normal processes of
metabolism, including growth and maintenance of health. It is known that the body is able to
produce part or even all of its requirements for some of the vitamins, Example: Vitamin D from
cholesterol and niacin from Tryptophan.
WATER SOLUBLE VITAMINS
Include the B- Vitamins and Vitamin C. They share few common properties besides their
solubility characteristics. Since they are water soluble excess can be excreted through urine.
Hyper-vitaminosis may not cause toxicity. Most of these vitamins act as coenzymes.
The B- Vitamins are essential and must be provided through diet: these include:
- Thiamine (Vit B1)
- Riboflavin (Vit B2 )
- Niacin (Nicotinic acid (or Nicotinamide)
- Pantothenic acid (Vit B5)
- Vitamin B6 (Pyrodoxine,pyridoxal,& Pyridoxamine)
- Biotin
- Vitamin B12 (Cobalamin)
THIAMINE
Thiamine is Vitamin B1. Addition of a pyrophosphate to thiamine (from ATP) converts it to
thiamine pyrophosphate, a molecule that is the coenzyme for all decarboxylations of -keto
acids.
Thiamine pyrophosphate
Mechanism of action - TPP contains two heterocyclic rings, a substituted pyrimidine and a
thiazole. The latter is the reactive moiety - specifically, the rather acidic carbon between the
sulfur and the nitrogen. This carbon forms a carbanion, which in turn, can attack the carbonyl
carbon of -keto acids, such as pyruvate, This compound undergoes nonoxidative
decarboxylation, with the thiazole ring acting as an electron sink, in forming a resonance-
stabilized ene-amine. Protonation gives a species called active acetaldehyde, or hydroxyethyl-
TPP.
Thus, in general terms, TPP functions in the generation of an activated aldehyde species, which
may or may not undergo oxidation as it is transferred to an acceptor.
Some enzymes that use TPP include pyruvate decarboxylase, pyruvate dehydrogenase,
branched chain α-keto acid dehydrogenase, α-keto glutarate dehydrogenase, transketolase.
Sources:
The good sources of Thamine are: Seeds, Nuts, Wheat, Legumenious plants (rich source) &
lean meat.
RDA: Minimum requirement 1.0mg for adults, infants and children 0.4-1.3mg
Requirment increases in conditions of Anoxia-shock, Hemorrhage, injury, illness, fever and
hyperthyroidism. Also increased carbohydrate in take, pregnancy and lactation.
Deficiency: Causes Beri-beri and related deficiency syndromes.
Mainly caused by carbohydrate rich diets. In such individuals TPP dependent reactions are
prevented, leading to accumulation of substrates like Pyruvate, Pentose sugars
Symptoms: There are two types Dry beri-beri not associated with edema and wet beri-beri
with edema, probably due to congestive cardiac failure and low plasma albumin. Symptoms
include Peripheral Neuropathy, Exhaustion and Anorexia. The signs may progress to edema
and Cardiovascular disorders, Neurological & muscular degeneration.
Wernicke Korsakoff syndrome which is frequently found in Alcoholics is associated with Thiamin
deficiency.
Diagnostic parameters: Erythrocyte transketolase activity decreases.
Thiamine excretion in Urine and Blood thiamine concentration decreases.
RIBOFLAVIN(VIT-B2)
Riboflavin, also known as vitamin B2, is a component of the flavin coenzymes, FAD and FMN.
It is composed of an isoalloxazine ring system linked to ribitol. The ability of the ring system of
riboflavin to exist as a semiquinone allows the flavin coenzymes to accept electrons either
singly or in pairs. NAD+
and NADP+
can only accept electrons in pairs.
It is mainly used in the energy metabolism of Sugars and Lipids. The activation of FMN and
FAD is an ATP-dependent.
Source: Meats, Nuts, Legumes, Milk, fish, egg etc.
RDA: 1.5-2.5mg for adults, infants 0.6mg, children 1.0-1.8mg
Deficiency: Lack of riboflavin in the diet causes a generally non fatal syndrome of inflammation
of the corner of mouth (angular stomatitis), painful glossitis of tongue (Purple) and Scaly
dermatitis.
A degree of photophobia may be due to its light sensitivity, because Riboflavin is colored,
fluorescent and decompose in visible light but heat stable.
Erythrocyte enzyme activity measurements (Glutathione reductase) is used to determine
Nutritional status of Riboflavin.
Niacin
Nicotinamide Nicotinic Acid
Niacin is not a vitamin in a strictest sense of the word, since it can be synthesized from
Tryptophan. However, conversion of Tryptophan to Niacin is relatively inefficient (60 mg of
Tryptophan is required to produce 1mg of Niacin) and occurs only after all the body
requirements for Tryptophan is met. Thus most people require dietary sources of both
Tryptophan and Niacin.
Niacin contains a substituted Pyridine ring and when gets activated forms NAD+ and its
phosphorylated derivative is NADP+
.which are co enzymes of many dehydrogenases.
Source: Milk, Lean meat, Unrefined grains, cereals and from Metabolism of Tryptophan.
RDA: Adults 17-21mg, infants 6mg.The requirement increases with increased intake of calories,
illness, severe injury ,infection ,burns, high corn (maize) diet, pregnancy and lactation.
Deficiency: Deficiency leads to Pellagra, a disease involving GIT and CNS.
The disease is characterized by intense irritation and inflammation of the mucous membranes of
the mouth and other parts of the GIT, leading to gastro- intestinal hemorrhage, Dermatitis,
Dementia & Diarrehea. (the “3-D’s” cardinal features). Skin lesiondevelop when exposed to
sunlight, become redend, thickened and becomes scaly. The patient develops gingivitis and
stomatitis (Tongue gets swollen) General effects of deficiency are Failure of growth, loss of
weight and anemia.
Vit B6 (Pyridoxine)
Pyridoxine Pyridoxal Pyridoxamine
Exists in three forms: Pyridoxine, Pyrodoxal & pyridoxamine and their corresponding
phosphates.
Pyridoxal phosphate (PLP)
Pyridoxal Phosphate
Pyridoxal phosphate participates in transaminations, decarboxylations, racemizations, and
numerous modifications of amino acid side chains. All pyridoxal phosphate-requiring enzymes
act via the formation of a Schiff base between the amino acid and coenzyme. A cation (a metal
or a proton) is essential to bridge the phenolate ion of the coenzyme and the imino nitrogen of
the amino acid. This bridging maintains the planarity of the structure, which is essential for
catalysis. The most important catalytic feature of the coenzyme is the electrophilic nitrogen of
the pyridine ring, which acts as an electron sink, drawing electrons away from the amino acid
and stabilizing a carbanion intermediate.It is also used for the synthesis of Neurotransmitter,
Serotonin and Nor-Adrenalin. Used as a component of Sphingolipids necessary for myelin
formation and Heme synthesis as well. Hypochromic microcytic anemia since PLP is requiredfor Heme synthesis.Deficiency in infants cause convelsions due to inactive glutamate
decarboxylase, GABA not formed there by impaired neurotransmission.
It is an essential component of Glycogen phosphorylase;it is covalently linked to a lysine residue
and stabilizes the enzyme.The conversion of Tryptophan to NAD also requires this co-factor.
Sources: Wheat, corn, egg yolk, Liver and muscle meat
RDA: 1.4-2.2mg for Adults, children 0.3-0.4mg.Patients with anti-tubercular treatment needs
more Vitamin B6.
Deficiency: usually is not common, but may result due to intake of drugs like Isoniazid and
contraceptives. Alcoholics also suffer from such deficiency. Isoniazid binds to pyridoxine and
makes it unavailable as a vitamin, causing peripheral neuropathy. oral contraceptives stimulate
the synthesis of the enzyme which require this vitamin, thus causing deficiency .
Biotin
Biotin Is a vitamin and a coenzyme commonly associated with enzymes performing
carboxylation reactions. Biotin is typically linked covalently to carboxylase enzymes through the
-amino nitrogen of lysine. Some of the enzymes that need Biotin for their activity include:
Acetyl-CoA carboxylase is the primary regulatory enzyme in fatty acid biosynthesis mediating
the following reactions:
Acetyl-CoA + ATP + HCO3
-
<=> Malonyl-CoA + ADP + Pi + H+
Pyruvate carboxylase is an enzyme of gluconeogenesis. It catalyzes formation of a carboxyl
group on pyruvate (using CO2) to make oxaloacetate.
Pyruvate + HCO3
-
+ ATP <=> Oxaloacetate + ADP + Pi + H+
Source: Normally synthesized by intestinal bacteria.
Found in all foods particularly: Liver, egg, peanuts & milkRDA: 100-200μg/day. Requirement increase in pregnancy and lactation. Patients on oral
antibiotics for a long period of time require more of this vitamin.
Deficiency:
Rare, since it is found in almost all food stuffs. But large consumption of raw egg white may lead
to deficiency of Biotin. Avidin, a glycoprotein in egg white binds tightly to biotin and makes it
unavailable for the necessary carboxylation reactions.
The symptoms in this case are: Dermatitis, Glossitis, Muscle pain, depression, alopecia (Loss of
hair), Loss of appetite and Nausea.
Vit B12 (Cobalamin).
The metal cobalt in vitamin B12 is coordinated with a tetrapyrrole ring system, called a corrin
ring, which is simiilar to the porphyrin ring of heme compounds. The cyanide attached to the
cobalt in the structure is an artifact of the isolation and is replaced by water or a hyrdoxyl group
in cells. The presence of cobalt and amide nitrogens gives B12 compounds the name
cobamides or cobalamins. Only two reactions occur to a significant extent in mammalian
metabolism: the synthesis of methionine from homocysteine. B12- requiring reactions involve either (1) methyl group transfer or (2) adenosylcobalamin-
dependent isomerizations. The isomerizations exchange a carbon-bound hydrogen with another
carbon-bound functional group.
Pernicious anemia arises from a B12 deficiency. Gastric tissue secretes a glycoprotein called
intrinsic factor, which complexes with ingested B12 in the digestive tract and promotes its
absorption through the small intestine into the blood stream. Pernicious anemia results from
insufficient secretion of intrinsic factor. Outlines a probable explanation for why failure to absorb
B12 leads to the deficiency of red blood cells that define anemias.
1. When B12 levels are low, flux through the methionine synthase reaction decreases but,
because adequate dietary methionine is usually available, protein metabolism is not
immediately disturbed.
2. Reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate continues
because this reaction is virtually irreversible.
3. Because methionine synthase is the only mammalian enzyme known to act on 5-
methyltetrahydrofolate, the decreased intracellular activity of this enzyme causes 5-
methyltetrahydrofolate to accumulate, at the expense of depleted pools of the other
tetrahydrofolate coenzymes. Thus, even though total folate levels may seem ample, there is
a functional folate deficiency, with insufficient levels of the formyl and methylene derivatives
needed for synthesis of nucleic acid precursors.
The action of B12 and folic acid, are interrelated. Deficiency of both produce similar signs and
symptoms and Anemias.
Source: Synthesized by Microorganisms
B12- requiring reactions involve either (1) methyl group transfer or (2) adenosylcobalamin-
dependent isomerizations. The isomerizations exchange a carbon-bound hydrogen with another
carbon-bound functional group.
Pernicious anemia arises from a B12 deficiency. Gastric tissue secretes a glycoprotein called
intrinsic factor, which complexes with ingested B12 in the digestive tract and promotes its
absorption through the small intestine into the blood stream. Pernicious anemia results from
insufficient secretion of intrinsic factor. Outlines a probable explanation for why failure to absorb
B12 leads to the deficiency of red blood cells that define anemias.
1. When B12 levels are low, flux through the methionine synthase reaction decreases but,
because adequate dietary methionine is usually available, protein metabolism is not
immediately disturbed.
2. Reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate continues
because this reaction is virtually irreversible.
3. Because methionine synthase is the only mammalian enzyme known to act on 5-
methyltetrahydrofolate, the decreased intracellular activity of this enzyme causes 5-
methyltetrahydrofolate to accumulate, at the expense of depleted pools of the other
tetrahydrofolate coenzymes. Thus, even though total folate levels may seem ample, there is
a functional folate deficiency, with insufficient levels of the formyl and methylene derivatives
needed for synthesis of nucleic acid precursors.
The action of B12 and folic acid, are interrelated. Deficiency of both produce similar signs and
symptoms and Anemias.
Source: Synthesized by Microorganisms
RDA: 3mg/day.
Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives. Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives. Pregnancy Increases the risk of Neural tube defects (a type of birth defect) and spontaneous
Abortions.
Folate deficiency is common in Alcoholics and in people who are on drugs like anti convulsants
and oral contraceptives.
Pantothenic Acid (Vit B 5) Coenzyme A.
Pantothenic acid is a vitamin that forms an essential part of the acyl-carrier moiety, coenzyme
A.
Coenzyme A (A for acyl) participates in the activation of acyl groups in general, including the
acetyl group derived from pyruvate. The coenzyme is derived metabolically from ATP, the
vitamin pantothenic acid, and -mercaptoethylamine. A free thiol on the last moiety is the
functionally significant part of the coenzyme molecule; the rest of the molecule provides enzyme
binding sites. In acylated derivatives, such as acetyl-coenzyme A, the acyl group is linked to
the thiol group to form an energy-rich thioester. The acylated forms of coenzyme A will be
designated here as acyl-CoA, and the unacylated form as CoA-SH.
The energy-rich nature of thioesters, as compared with ordinary esters, is related primarily to
resonance stabilization. Most esters can resonate between two forms. Stabilization involves Pi-
electron overlap, giving partial double-bond character to the C-O link. In thioesters, the larger
atomic size of S (as compared with O) reduces the Pi-electron overlap between C and S, so that
the C-S structure does not contribute significantly to resonance stabilization. Thus, the thioester
is destabilized relative to an ester, so that its G of hydrolysis is increased.
The lack of double-bond character in the C-S bond of acyl-CoAs makes this bond weaker than
the corresponding C-O bond in ordinary esters, in turn making the thioalkoxide ion (R-S-) agood leaving group in nucleophilic displacement reactions. Thus, the acyl group is readily
transferred to other metabolites, as occurs, in fact, in the first reaction of the citric acid cycle.
Some of the common metabolic reactions involving Coenzyme A are shown below.
1. Pyruvate + NAD+
+ CoA-SH <=> Acetyl-CoA + NADH + CO2 (catalyzed by Pyruvate
Dehydrogenase).
2. Acyl-CoA + Carnitine <=> Acyl-Carnitine + CoA-SH (catalyzed by Carnitine
Acyltransferase I)
Sources: Eggs, Liver, Animal tissue, Whole grain cereals, Yeast and Legumes
RDA: 4-7mg/day
Deficiency: rare due to its wide distribution
The burning foot syndrome in prisoners which is associated with reduced capacity for
acetylation is ascribed to pantothenic acid deficiency.
Vit C (Ascorbic Acid)
Vitamin C is a water-soluble vitamin. Collagen is unusual in its widespread modification of
proline to hydroxyproline and lysine to hydroxylysine. Most of the hydrogen bonds between
chains in the triple helix are from amide protons to carbonyl oxygens, but the OH groups of
hydroxyproline also seem to participate in stabilizing the structure. Hydroxylysine residues in
collagen serve to form attachment sites for polysaccharides.
The hydroxylation reactions in collagen involve vitamin C. A symptom of extreme vitamin C
deficiency, called scurvy, is the weakening of collagen fibers caused by the failure to
hydroxylate proline and lysine.
In general hydroxylation reactions require Vit C.
Example: Hydroxylation of cholesterol.
Functions:
• Collagen biosynthesis
• Degradation of Tyrosine
• Absorption of Iron
• Steroidogenesis
• Adrenaline synthesis
• Bile acid formation
• Degradation of tyrosine
• Bone mineral metabolism
• Potent anti oxidant
WBC’s are rich in vit C and plays an important role in Immunity.
Source: Citrus fruits, Potato, tomato & green vegetables
RDA: 60mg/day
Deficiency: scurvy symptoms are spongy gums and bleeding of gums due to defective collagen
synthesis.
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