312 JOHN M. BUCHANAN 



S 



N NH COOH 



CH 2 

 CH, 

 N' ,Z^ «C-CH,-NH— € >— CO-NH — CH 



C NH 



OH 



5,6,7,8-TETRAHYDROFOLIC ACID (FH 4 ) 



COOH 



COOH 

 CH, 



CH 2 



CO-NH-CH 



COOH 



N 5 ,N-ANHYDROFORMYL TETRAHYDROFOLIC ACID 



COOH 



N 5 ,n'- METHYLENE TETRAHYDROFOLIC ACID 

 Fig. 5. Structure of formylated derivatives of tetrahy drofolic acid. (*N b ,N 10 

 anhydroformyltetrahydrofolic acid has also been called A /5 ,A ri0 -methenyltetra- 

 hydrofolic acid.) 



purple-colored product. The enzyme, glycinamide ribonucleotide trans- 

 formylase, has been purified approximately sixtyfold from chicken liver 

 and has been separated completely from the transformylase responsible for 

 the incorporation of formate carbon into position 2 of the purine ring. 45 

 The enzyme is sensitive to metal impurities and is inhibited about 50 % by 

 a concentration of cupric ion of 10~ 4 M. This inhibition may be relieved 

 by the addition of cyanide. 



With crude preparations of enzyme, both Af 5 ,^ 1 ^anhydroformyltetra- 

 hydrofolic acid (Fig. 5) and iV 10 -formyltetrahydrofolic acid may donate 

 formyl groups to glycinamide ribonucleotide. The fact that both forms are 

 utilized is due to the presence of cyclohydrolase, an enzyme which carries 

 out the hydration of the A^iV^-anhydroformyltetrahydrofolic acid to the 



46 L. Warren and J. M. Buchanan, J. Biol. Chem. 229, 613 (1957). 



