VITAMIN AND GROWTH FACTOR RESEARCH 



fermentation residues. It was noted that these concentrates re- 

 placed pantothenic acid for some organisms (e.g., L. arabinosus) 

 but not for others (e.g., Saccharomyces carlsbergensis), and, con- 

 versely, very large amounts of pantothenic acid replaced the 

 unidentified substance as a growth factor for L. bulgaricus. Thus 

 the substance appeared to be a combined form of pantothenic 

 acid, and further work revealed its structure to be that illus- 

 trated in formulas VIII and IX. These findings came just as 

 the structure of coenzyme A (formula X) was under active 

 investigation, and just as Lynen had shown the acyl- transferring 

 role of coenzyme A to take place via a sulfhydryl grouping. The 

 postulate (8,72) that pantetheine represented the then chemically 

 unidentified portion of coenzyme A was rapidly borne out by the 

 enzymatic resynthesis of coenzyme A from pantetheine and 

 adenosine triphosphate (16). This was the first recognition of 

 the occurrence of the j3-mercaptoethylamine residue in nature. 

 The fact that the growth factor for L. bulgaricus occurs naturally 

 in several chromatographically distinct forms was shown to result 

 from the presence of a variety of mixed disulfides formed by 

 oxidative cross-linking between pantetheine and other sulfhydryl 

 compounds (5). 



Just as pyridoxal or pyridoxamine and folinic acid are more 

 closely related to the coenzyme form of these vitamins than 

 pyridoxine or folic acid, so then is pantetheine intermediate 

 between coenzyme A and pantothenic acid. In each case, a 

 specific requirement for these compounds by certain organisms 

 appears to result from inability or a markedly lowered ability 

 to eflfect conversion a in the sequence : 



pvTidoxine 1 



folic acid > > { 



pantothenic acid J 



It sometimes happens that conversion b is also diflficult. 

 We have referred to the fact that for some lactic acid bacteria 

 pyridoxamine phosphate is many hundred times more active 

 than pyridoxamine or pyridoxal in promoting growth. Simi- 

 larly, for a strain of Treponema pallidum neither pantothenic acid 



97 



pyridoxal 1 ^ fpyridoxal phosphate 



folinic acid[ > •^coenzyone F 



pantetheine J (coenzyme A 



