Pfizer Handbook of Microbial Metabolites 550 



The two forms are interconvertible and this oxidation- 

 reduction equilibrium probably is mediated by an enzyme 

 with triphosphopyridine nucleotide (TPN) as the pros- 

 thetic group. 



Formate added as a substrate is, then, activated in this 

 way. The N^"-formyl group also can be furnished by 

 glycine, either by way of glyoxylic acid'^ ^^ or by way of 

 S-aminolevulinic acid.^^ ^'' ^^ The equations are: 



transam- 

 ination [O] 



H2N— CH2— COOH , OHC— COOH * 



Glycine Glyoxylic 



Acid 



COo -f Ni°-Formyltetrahydrofolic Acid 

 and 



o 00 



li NH3 II II 



H,N— CH,— C— CH,— CH2— COOH . ^ ' H— C— C— CH,.— CHo— COOH 

 6-Aminolevulinic Acid a-Ketoglutoraldeiiyde 



[O] 

 ^ HOOC— CH>— CH2— COOH + N'o-Formyltetrahydrofolic Acid 



Succinic Acid 



Once formed "active formate" is the formylating agent 

 in certain metabolic reactions. The important formyla- 

 tions by this agent which have been discovered to date are 

 the two formylations already noted in the biosynthetic 

 route to the purines. Thus glycineamide ribotide is 

 formylated to furnish C-8 of the purine nucleus and, later, 

 5-amino-4-imidazolecarboxamide ribotide is formylated to 

 furnish C-2 of the purine nucleus. 



^ Henry I. Nakada and Sidney Weinhouse, Arch. Biochem. and 

 Biophijs. 42 257 (1953). 



1^' Sidney Weinhouse in W. D. McElroy and H. B. Glass (Editors), 

 "Amino Acid Metabolism," Johns Hopkins Press, Baltimore, 1955, pp. 

 637-57. 



" David Shemin, ibid., p. 727. 



^^ David Shemin, Tessa Abramsky and Charlotte S. Russell, /. Am. 

 Chem. Soc. 76 1204 (1954). 



'"^ Irving Weliky and David Shemin, Federation Proc. 16 268 

 (1957). 



