FERMENTATIONS OF NITROGENOUS COMPOUNDS 85 



other coenzyme form of folic acid. The initial step is a 

 reversible transfer of the formimino group to THFA. The 



Formiminoglycine + THFA ^=^: 



Glycine + 5-Formimino-THFA (13) 



first evidence for this reaction consisted in the demonstra- 

 tion by Sagers et al. 67 that certain cell-free extracts catalyze 

 an exchange between C 14 -glycine and formiminoglycine 

 which is more rapid than the formation of ammonia and 

 formate. Recently Rabinowitz and Pricer 68 have purified 

 the enzyme catalyzing this reaction and have partially char- 

 acterized the product as 5-formimino-THFA. They have 

 also shown that a second enzyme removes ammonia from 

 5-formimino-THFA to give 5,10-anhydroformyl-THFA (an- 

 hydroleucovorin) which in turn is converted by a third 

 enzyme to 10-formyl-THFA. 



The decomposition of 10-formyl-THFA can be coupled 

 with the formation of ATP by the following reversible 

 reaction: 



10-Formyl-THFA + ADP + P, ^±: 



THFA + HCOOH + ATP (14) 



Perhaps this reaction also consists of more than one step 

 since it involves an activation of orthophosphate (P^) and 

 a transfer of the phosphate group to ADP. 



The above reactions account satisfactorily for the decom- 

 position of xanthine to glycine, fprmate, carbon dioxide, 

 and ammonia. However, in the fermentation of purine by 

 living cells of CI. acidi-urici very little glycine and formate 

 accumulate; the main organic product is acetate. There- 

 fore it is necessary to account for the conversion of glycine 

 and formate or their known precursors to acetate. 



