Pfizer Handbook of Microbial Metabolites 516 



atom of glycine, the /3-C-atom of serine and the C-atom 

 of formate can all serve as donors at least indirectly.^*'' ^^ 

 There is a vitamin Bio requirement for the conversion of 

 formate to the thymine methyl group in Lactobacillus 

 leichmannii, and the pathway does not involve methionine 

 or a hydroxymethyl group. ^^ It has been suggested that 

 since vitamin Bj2 coenzymes are required to promote the 

 equilibrium 



HOOC— CH2— CH2— CH— COOH ^ HOOC— CH— CH— COOH 



I 1 I 



NHo CH3 NH2 



Glutamic Acid j3-Methylaspartic Acid 



/3-methylaspartic acid may replace aspartic acid as an 

 intermediate in thymine biosynthesis.^'' 



An alternate pathway of pyrimidine biosynthesis in- 

 volving dihydrouracil, a member of the catabolic route, 

 has been suggested. *° 



O O 



It II /"^ 



An/* /-h\ 



OH O H NH2 



4,5-Dihydrouracil 4,5-Diaminouracil 



The entire subject of the enzymic synthesis of pyrim- 

 idines has been reviewed.^^ 



4,5-Diaminouracil has been detected as a metabolite of 

 Eremothecium ashbyii and suggested as an intermediate 

 in riboflavin biosynthesis. ^- 



■^'^ David Elwyn and David B. Sprinson, 7. Biol. Chem. 207 467 

 (1954); idem., J. Am. Chem. Soc. 72 3317 (1950). 



•"J. R. Totter, Elliott Volkin and C. E. Carter, J. Am. Chem. Soc. 

 73 1521 (1951); J. R. Totter and Audrey N. Best, Arch. Biochem. 

 and Biophys. 54 318 (1955). 



■^^ James S. Dinning, Barbara K. Allen, Ruth Young and Paul L. 

 Day, J. Biol. Chem. 233 674 (1958). 



■^^ H. D. Isenberg, E. Seifter and J. I. Berkman, Biochim.. et Biophys. 

 Acta 39 187 (1960). 



^" Lewis C. Mokrasch and Santiago Grisolia, Biochim,. et Biophys. 

 Acta 27 227 (1958). 



•" Peter Reichard, Advances in Enzymology 21 263-294 (1959). 



*-T. W. Goodwin and D. H. Treble, Biochem. J. 67 lOp (1957). 



