FACTORS INFLUENCING B VITAMIN REQUIREMENTS 289 



(5) Pantothenic Acid 



Pantothenic acid is known to occur in the form of the free acid, as 

 coenzyme A, in one or more bound forms, and possibly in the form of 

 conjugates with one or more amino acids (glutamic acid particularly has 

 been suggested). In addition, certain lower organisms at least can utilize 

 either the /^-alanine or the pantoyl fraction of the molecule in lieu of 

 pantothenic acid 120,1 - 7 ; and an amino acid which has recently been 

 indicated as occurring naturally has been suggested as a precursor of 

 pantoic acid, and may have pantothenic acid activity. 128 Coenzyme A is 

 apparently available to animals, but /^-alanine is inactive for at least 

 rats and chicks, and probably all higher animals. Pantothenyl alcohol, a 

 synthetic compound presumably not occurring in nature, is reported to be 

 utilized by humans as readily as pantothenic acid, and may in some cases 

 be even more effective, perhaps due to its apparently greater stability to 

 acid. 129-132 It cannot be oxidized by bacteria to the acid, however, and so 

 is inactive in supporting bacterial growth. 



(6) Biotin 



Whereas biotin may have a large number of stereoisomers, there is little 

 evidence to indicate that they occur naturally. There are reputed to be, 

 however, as yet unelucidated avidin uncombinable forms, and bound 

 forms. The bound forms which occur naturally seem to be readily utilized 

 by most animals. There is also some evidence for the existence of a biotin 

 coenzyme which is more active than biotin. 132a O-Heterobiotin (oxybiotin) 

 which is a synthetic analogue, and desthiobiotin, which may possibly 

 occur naturally, have however been studied quite extensively and com- 

 pared to biotin carefully as regards their potency. Other substances with 

 structures as yet unknown, and some with structures unlike that of biotin 

 (oleic acid) substitute for biotin in some lower forms of life. 133 



McCoy et al. 134 have shown that DL-oxybiotin is about 17 per cent as 

 effective as biotin for the chick. It is 25 per cent as active as D-biotin for 

 Saccharomyces cerevisiae and Lactobacillus casei, and 50 per cent for 

 L. arabinosus. 1 * 5 It is inactivated by avidin, and its effect for L. casei is 

 inhibited by desthiobiotin. DL-Oxy biotin prevents chick dermatitis at 

 levels of about 20 ^g per 100 g diet. 130 Using growth and the disappearance 

 of skin lesions as criteria, DL-oxybiotin is found to be only 4 per cent as 

 active as D-biotin in curing egg-white injury in the rat. 137 



Tatum has suggested that desthiobiotin functions in the biosynthesis 

 of biotin. 138 Desthiobiotin is one-twentieth as active as D-biotin in curing 

 egg-white injury in rats. 135 Wright et al. have recently isolated a crystal- 

 line biotin-protein complex. 191 



