Chemical Substances of Vitamin B Complex | Nutrition | Organisms | Biology

The vitamin of B complex comprises some of chemical substances. They are: 1. Lipoic Acid 2. Pantothenic Acid 3. Folic Acid 4. Biotin 5. Choline and Lipotropic Factor 6. Para-Amino-Benzoic Acid 7. Inositol.

1. Lipoic Acid (Thioctic Acid):

For a certain micro-organism and protozoa, α-lipoic acid is a growth factor which is usually classified among the vitamin B complex. This acid is also known as acetate-replacement factor, pyruvate oxidation factor or protogen.

Chemistry:

It is sulphur-containing fatty acid and chemically it is 6, 8-dithio-octanoic acid.

Properties:

This compound is soluble in fat.

Distribution:

Widely distributed in natural sources.

Functions:

Lipoic acid is required along with thiamine and some other members of vitamin B in the oxidative decarbox­ylation of pyruvic acid to acetyl CoA and α-ketoglutaric acid to succinyl CoA.

Deficiency Signs:

Has not been shown to be required in the diet of higher animals and deficiency signs not yet demonstrated.

2. Pantothenic Acid (Vitamin B₃) (Chick Antidermatitis Factor, Filtrate Factor):

Historical Review:

In 1901, a growth factor for yeast, bios was described by Wildiers. In 1933 Williams and his coworkers isolated the crystalline product and called it pantothenic acid because of universal distribution. It was synthesised in 1940 by Stiller and others.

Chemistry:

It is peptide-like compound of β-alanine and α-ϒ-dihydroxy-β, β-dimethyl butyric acid. The empirical formula of vitamin B₃ is C₉H₁₇O_sN.

[HO.CH₂.C(CH₃)₂.CHOH.CO.NH.CH₂.CH₂.COOH.]

Properties:

The free acid is viscous, yellow oil, soluble in water and ethyl acetate but insoluble in CHCI₃ It is heat-labile and destroyed in acid and alkali. Its calcium salt is a white, crystalline substance, highly soluble in water and hygroscopic and insoluble in alcohol. It is quite stable, although autoclaving destroys activity.

Distribution:

It is widely distributed in small amounts.

i. Animal Sources:

Liver, kidney, egg-yolk, yeast, milk, etc. are the rich sources of this vitamin.

ii. Vegetable Sources:

Molasses, wheat bran, peas, sweet potatoes, etc., contain this vitamin in appreciable amount. It has also been produced synthetically. Blood contains 19—32 µ gm per 100 ml.

Functions:

The physiologically active form of pantothenic acid is coenzyme A (CoA). It is essential for several basic reactions of metabolism.

i. Acetyl CoA, also known as active acetate, takes part in the citric acid (TCA) cycle, in combination with choline forms acetylcholine and also acts as an intermediate in the biosynthesis of cholesterol, fatty acids, etc.

ii. Coenzyme A plays an essential part in lipid metabolism. Activation which occurs by formation of a coenzyme A derivative is the first step in fatty acid oxidation.

iii. Pantothenic acid is not present mainly in CoA. A good amount of pantothenic acid is present in the protein- bound form. This protein-bound pantothenic acid is the acyl-carrier protein (ACP) and is required for the biosynthesis of fatty acids.

iv. Although this coenzyme is required in the biosynthesis of fatty acids, but coenzyme A is mainly concerned with fatty acid catabolism.

v. Being a precursor of cholesterol, acyl coenzyme A may produce steroid hormone.

vi. CoA in combination with succinate forms active succinate and helps in the biosynthesis of haemoglobin.

vii. It might activate some amino acids.

Deficiency Signs:

Dermatitis, fatty liver, degeneration of spinal cord, myelin degeneration of peripheral nerves, and involution of thymus in chicks occur by the deficiency of this vitamin. Various tissues are also affected, including gastro­intestinal disturbances, alopecia, and cornification of the skin and hypofunction of adrenal cortex.

Daily Requirement:

Not exactly known. Average daily diet contains 10 mgm which satisfies this vitamin requirement.

3. Folic Acid (Pteroylglutamic Acid) (Fermentation Residue Factor):

Historical Review:

The existence of this nutritional factor was suggested by Day. It was named folic acid (L. folium) by Mitchell, Snell and Williams, because of its isolation from spinach leaf. The chemical structure was established in 1945. It has also been known as vitamin M, vitamin B_c, Liver Lactobacillus casei factor and Streptococcus lactis R (SLR) factor.

Chemistry:

Folic acid is a group of chemically different compounds. The simplest form of pteroylglutamic acid (PGA) contains a pterin derivative residue connected to para-amino-benzoic acid and glutamic acid.

Folic acid or folacin is converted into tetrahydro derivative in the body which after taking up a formyl (CHO) group forms folinic acid also known as citrovorum factor (CF).

Properties:

It is a yellow compound, slightly soluble in water and destroyed by light. It is soluble in dilute alcohol and can be precipitated as barium or lead salt.

Distribution:

Liver, kidney, green-leafy vegetables and cauliflower are good source of this vitamin.

Function:

i. Folic acid acts as a coenzyme (coenzyme F) in the transfer of formyl and hydroxymethyl groups in different biological systems (e.g. in the biosynthesis of purine, synthesis of the methyl group of methionine etc.)

ii. It is indispensable for the synthesis of deoxyribonucleic acid in the nuclei of the cells. Takes part in the formation and maturation of red cells. Along with Vitamin B₁₂ it helps in the synthesis of nucleic acid. Deficiency causes disturbances in the synthesis of deoxyribonucleic acid (DNA) and metabolism of the nucleated red cells resulting in megaloblastic or macrocytic anemia.

iii. It is used in the treatment of megaloblastic anaemia.

Deficiency Signs:

In rats and monkeys – Arrested growth, anaemia, leucopenia and agranulocytosis. In man-Megaloblastic anae­mia especially occurring during pregnancy.

Daily Requirement:

Not exactly known. Average daily diet of adults contains about 50 micro-gram, which seems to be adequate.

4. Biotin (Vitamin H) (Anti-Egg-White-Injury Factor):

Historical Review:

In 1916, Bateman observed that a diet containing high percentage of egg-white was toxic to animals. In 1941, avidin the protein isolated from egg-white was found to prevent absorption of biotin. Allison and others (1933) isolated another growth factor and named it coenzyme R which was later found to be iden­tical to biotin. Its structure was identified in 1942 and synthesized in 1943.

Chemistry:

Biotin is a heterocyclic, s-containing mono-carboxylic acid, a valeric acid derivative containing two five-sided rings (thieno and imidazole) fused together. Biotin acts as coenzyme for carboxylase enzyme that helps in carbon dioxide fixation. It is suggested that biotin co­enzyme is tightly bound to enzyme protein by an amide linkage between the biotin carboxyl group and the termi­nal (epilson) nitrogen of the lysine in the enzyme protein (apoenzyme) (Fig. 11.8). In naturally-occurring biotin. Biocytin has been identified as a lysine biotin conjugate – Ɛ-N-biotinyl lysine.

Properties:

It is soluble in water and alcohol, heat-stable and resistant to acids and alkalis. It contains sulphur.

Distribution:

Present in all common articles of food – spe­cially in yeast, egg-yolk kidney, liver, cauliflower, peas etc. Raw egg white contains avidin which antagonizes biotin and thus the animal suffers from this vitamin deficiency. Hence raw egg-white is antibiotin in nature.

Functions:

i. Biotin acts as coenzyme for carboxylase, so as to help in carboxylation reactions (CO₂ fixation), viz., in urea formation and bio-synthesis of pyrimidines and fatty acids. It also helps in deamination of threonine, serine and aspartic acid.

ii. An important function of biotin is in the coenzyme activity related to carbamyl phosphate synthesis and reaction related to it.

iii. In micro-organism, biotin is related to purine synthesis.

iv. Biotin enzyme plays a specific role in lipid synthesis in animals.

v. Prevents dermatitis in rats and dogs.

Deficiency Signs:

In dogs and rats – dermatitis.

Experimental deficiency in man causes:

i. A peculiar dermatitis of the extremities, pallor of skin and mucous membranes.

ii. Symptoms resembling thiamine deficiency.

iii. Rise of blood cholesterol occurs.

iv. In rats, deficiency produces spectacle-eyed appearance; thinning of fur (alopecia) in mouse, pigs etc.; and perosis or slipped tendon disease in fouls.

v. Deficiency does not occur normally but may be induced either by:

i. Feeding raw egg-white which contains an antivitamin avidin able to form a non-absorbable complex with biotin.

ii. Administration of sulpha drugs which interferes with normal synthesis of this vitamin by micro­organisms in the intestine.

Daily Requirement:

In human beings it is 150-300 micro-grams per day on the average. Average daily diet contains sufficient amount.

5. Choline and Lipotropic Factor:

Choline and methionine exert lipotropic action.

Properties:

It is water-soluble and a component of lecithin, acetylcholine, and other phospholipids. Essential for rats and chicken, if intake of methionine is low.

Distribution:

Rich sources are butter, nervous tissues, eggs etc.

Functions:

i. It has got a lipotropic action.

ii. It required for synthesis of lecithin, sphingomyelin, acetylcholine etc.

iii. It acts as a methyl donor in transmethylation.

Deficiency Signs:

i. It produces fatty liver in rats

ii. Causes haemorrhagic necrosis in kidneys

iii. Anaemia,

iv. Hypoproteinemia in mammalian species.

Daily Requirement:

Not essential for man, because it is freely synthesized in the body.

6. Para-Amino-Benzoic Acid (PABA):

Chemistry:

Empirical formula (COOH-C₆H₄NH₂) structurally similar to sulphonamides.

Properties:

It is white crystalline substance and slightly soluble in water but highly soluble in alcohol.

Distribution:

It is widely distributed in animal tissues and also found in wheat germ, rice bran and polishings and milk.

Functions:

i. Essential for the growth of micro-organisms. It has similar chemical structure as that of sulphonamides so it prevents the bacteriostatic properties of the drug.

ii. It maintains growth and lactation in albino rats and preserves hair colour in black rats.

iii. It forms a portion of folic acid.

iv. Its role in human nutrition is not definitely established.

Deficiency Signs:

i. Might be responsible for achromotrichia in man due to changes in intestinal microflora.

ii. Production of gray hair has also been postulated.

7. Inositol (Mouse Anti-Alopecia Factor):

Chemistry:

Hexahydroxycyclohexane, Empirical formula (CH₂O)₆

Properties:

It is soluble in water and sweet taste. (But not a carbohydrate). The natural variety is optically inactive and is known as mesoinositol.

Distribution:

Rich sources are muscles (hence called muscle sugar), liver, kidney, brain, etc. In cereals it is phytic acid (hexophosphate).

Functions:

i. It has a lipotrophic action like choline in rat and might play some part in fat metabolism.

ii. In hamsters, inositol is essential for normal reproduction.

iii. In mice, chicks and rats, it is required for normal growth.

iv. Its function in man is not definitely known.

Deficiency Signs:

i. Alopecia in mice.

ii. A peculiar eye in rats known as ‘spectacle eye’ condition.

Daily Requirement:

Human requirement not known, but daily diet contains about 1.0 gm which seems enough.