V. BIOGENESIS 627 



activity.^" Thepantoic lactone portion of the pantothenic acid molecule has 

 also been modified in many ways, all of them resulting in great loss of 

 activity.^ The only modifications of pantothenic acid which retain appre- 

 ciable, but by no means full, activity are hydroxypantothenic acid^° and 

 methylpantothenic acid.^' ^° It is not known whether modifications in vivo 

 account for all or part of the activity of these analogs. 



V. Biogenesis 



SAMUEL LEPKOVSKY 



Microorganisms differ in their ability to synthesize pantothenic acid. 

 Some are capable of its total synthesis. This has been demonstrated by the 

 rumen microorganisms in cattle and sheep. ^ Its synthesis also takes place 

 in the intestinal tract of rats, apparently by the bacteria in the cecum. Some 

 organisms can produce only the pantoic lactone fragment but not fi- 

 alanine,^' whereas others can synthesize /3-alanine but not pantoic 

 lactone.^' 



/^-Alanine is apparently formed by the decarboxylation of aspartic acid.' 



COOH 



— ^'-> NH2CH2CH2COOH 



;8-Alanine 



/3-Alanine is then coupled with pantoic acid to form pantothenic acid. 

 The steps in the biosynthesis of pantoic acid remains to be worked out. 



10 R. J. Williams, Advances in Eiizymol. 3, 253 (1943). 



' L. W. McElroy and H. Goss, /. Nutriiion 21, 405 (1941). 



2 R. J. Williams, R. E. Eakin, E. Beerstecher, Jr., and W. Shive, The Biochemistry 

 of the B Vitamins. Reinhold Publishing Corp., New York, 1950. 



^ H. R. Rosenberg, Chemistry and Physiology of the Vitamins. Interscience Pub- 

 lishers New York, 1945. 



