FORMIC ACID AND FORMATE METABOLISM 287 



to be an especially effective source of carbons 2 and 8 of uric acid in pigeons. 



202,203 



f. Miscellaneous Compounds Related to Formate. Acetone (Reaction 

 11) is able to contribute the carbon of its methyl groups to the methyl 

 groups of choline. Sakami'"* is of the opinion that this transfer involves 

 the formation of a formate-like intermediate. 



Stekol et al}'^'^ reported that formate or glycine is involved in the syn- 

 thesis of cysteine. In deficiency of folic acid or vitamin B12, this synthesis 

 was found to be depressed. 



Serine can originate from carbon-^ of threonine by way of glycine, ^"^ 

 and formate from tryptophane via formylkjaiurenine.^"^-^"^ It is thus 

 evident that four of the so-called essential amnio acids, namely, histidine, 

 methionine, threonine, and tryptophane, are sources of the one-carbon 

 intermediate, formate, which appears to be necessary in the synthesis of 

 many essential biologic products. 



{4) Factors Involved in Formate Utilization 



ggj.g208 prepared a cell-free extract from pigeon liver which was able to 

 catalyze the anaerobic incorporation of formate-C^^ into cystathionine, 

 methionine, the /3-carbon of serine, and the ureide carbon of purines. It 

 was shown that all reactions were catalyzed indi\'idually; serine and cysta- 

 thionine were not believed to be intermediates in the conversion of formate 

 to the methyl group of methionine. Homocysteine markedly increased the 

 incorporation of formate not only into serine and purines, but also into the 

 methionine methyl groups. When compounds are added which promote 

 the formation of different formate acceptors, the relative distribution of 

 formate between the several compounds listed above may be altered. It 

 is suggested that an intermediate formed from homocysteine and formate 

 is a common precursor in the serine, purine, and methionine synthesis. 

 Berg-"^ also reported that one or more heat-labile factors are required for 

 the conversion of formate to methionine methyl groups. 



Arnstein and Neuberger-°^ found that, when young rats were fed C^^- 

 containing precursors, the radioactivity of the methionine methyl groups 



^' D. B. Sprinson and D. Rittenberg; unpublished results cited by D. B. Sprinson, 

 Ahst. Am. Chem. Soc, 119th Meeting, (Boston, Mass., April, 1951), 11C-12C. 

 ^' W. Sakami, /. Biol. Chem., 187, 369-378 (1950). 

 205 H. L. Meltzer and D. B. Sprinson, Federation Proc, 9, 204 (1950). 

 20s W. E. Knox and A. H. Mehler, /. Biol. Chem., 187, 419-430 (1950). 

 =»' A. H. Mehler and W. E. Knox, /. Biol. Chem., 187, 431-438 (1950). 

 ^^ P. Berg, /. Biol. Chem., 205, 145-162 (1953). 

 209 H. R. V. Arnstein and A. Neuberger, Biochem. J., 55, 259-271 (1953). 



