PARA-AMINOBENZOIC ACID
A. History: Ansbacher demonstrated that depigmentation of the hair (achromotrichia) in mouse could be cured by feeding rice polishings or by adding p-aminobenzoic acid (PABA) to the diet. PABA also appeared essential for the growth of rat and chick and also for bacterial multiplication.
B. Occurrence:PABA is widely distributed in nature. The good sources are liver, yeast, rice bran and whole wheat. PABA occurs in conjugated form as a part of folic acid and its derivatives
C. Structure: he structural formula of p-aminobenzoic acid
D. Properties:PABA is a white crystalline substance. It is sparingly soluble in cold water but freely soluble in hot water and alcohol.
E. Metabolism: Woods, for the first time, observed that PABA blocks the bacteriostatic properties of sulfanilamide . PABA is synthesized from shikimic acid via chorismic acid.
F. Deficiency: The deficiency of PABA affects adversely the growth and the maintenance of a normal fur coat in rats.
G. Human requirements: There is, at present, no evidence that PABA is an essential dietary factor for man.
ALPHA-LIPOIC ACID
A. History: Ansbacher demonstrated that depigmentation of the hair (achromotrichia) in mouse could be cured by feeding rice polishings or by adding p-aminobenzoic acid (PABA) to the diet. PABA also appeared essential for the growth of rat and chick and also for bacterial multiplication.
B. Occurrence:PABA is widely distributed in nature. The good sources are liver, yeast, rice bran and whole wheat. PABA occurs in conjugated form as a part of folic acid and its derivatives
C. Structure: he structural formula of p-aminobenzoic acid
D. Properties:PABA is a white crystalline substance. It is sparingly soluble in cold water but freely soluble in hot water and alcohol.
E. Metabolism: Woods, for the first time, observed that PABA blocks the bacteriostatic properties of sulfanilamide . PABA is synthesized from shikimic acid via chorismic acid.
F. Deficiency: The deficiency of PABA affects adversely the growth and the maintenance of a normal fur coat in rats.
G. Human requirements: There is, at present, no evidence that PABA is an essential dietary factor for man.
ALPHA-LIPOIC ACID
A. History: Lipoic acid is a relatively newly-discovered factor. This factor supports the growth of a number of bacteria and protozoa. 
It has been variously called as pyruvate oxidation factor (POF) or acetate replacement factor or protogen. Lester J. Reed et al (1951) isolated this factor in crystalline form from the insoluble residue of liver. When first isolated, lipoic acid was believed to be a B-vitamin because of its coenzyme function.However,the current opinion is in favour of treating lipoic acid as a pseudovitamin since it is synthesized by most animals.
B. Occurrence: It is found in many biologic materials including yeast and liver.
It has been variously called as pyruvate oxidation factor (POF) or acetate replacement factor or protogen. Lester J. Reed et al (1951) isolated this factor in crystalline form from the insoluble residue of liver. When first isolated, lipoic acid was believed to be a B-vitamin because of its coenzyme function.However,the current opinion is in favour of treating lipoic acid as a pseudovitamin since it is synthesized by most animals.B. Occurrence: It is found in many biologic materials including yeast and liver.
C. Structure: α-lipoic acid (C8H14O2S2) is a cyclic disulfide, derived from 6, 8-dimercapton-caprylic acid
D. Properties: Lipoic acid is an exception of the vitamins of B series in that it is fat-soluble rather than water-soluble.
E. Metabolism: Lipoic acid acts as a catalytic agent for the oxidative decarboxylation of pyruvic acid and α-ketoglutaric acid by certain microorganisms. It is probably a coenzyme or part of a coenzyme, called as lipothiamide pyrophosphate (LTPP), for this reaction.
F. Deficiency: A deficiency of lipoic acid usually does not occur since it is synthesized by most animals.
G. Human requirements: α-lipoic acid is not an essential factor of the diet.
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