286 VI. ACETIC, FORMIC, AND PROPIONIC ACIDS 



berger,^^^'^^^ found that a deficiency in vitamin B12 had Httle or no effect 

 upon the above synthesis. Vitamin B12 is apparently required for the 

 conversion of glycine to serine. "^■^^■^-^^^ Serine forms the aminoethanol 

 moiety of choline.^^^-^^'' Since it is well knowTi that formate participates 

 in the synthesis of serine from glycine, it is evident that more formate 

 carbon would appear in the choline molecule than can be accounted for in 

 the methyl groups. 



Although the weight of evidence would seem to indicate that \'itamin 

 B]2 does not appreciably influence the conversion of the j8-carbon of serine 

 to choline-methyl groups, it is apparently concerned with the conversion 

 of glycine to a form suitable for the acceptance of "formate" to yield 

 serine. This ^dtamin may be needed for the activation of another com- 

 pound which reacts with glycine to form serine. It is possible that sulf- 

 hydryl compounds such as homocysteine or glutathione are required; 

 according to Dubnoff,^^^-^^^ \'itamin B12 is necessary to maintain these 

 reducing compounds in their reduced state. 



Moreover, folic acid does not take part in the formation of cystathionine 

 from homocysteine and serine. ^^* There is considerable question, there- 

 fore, as to whether or not folic acid or CF plays a definite role in serine 

 metabolism.'"" One may conclude that folic acid functions in the bio- 

 synthesis of choline in the reactions leading to the synthesis of methio- 

 nine,"^ and in reactions involved in the synthesis of L-serine, which is the 

 precm'sor of the aminoethanol moiety."^ 



e. Formate in the Catabolism of Histidine (Reaction 1£). The reaction 

 discovered by Edlbacher and Kraus^^^ in 1930 without the use of isotopes, 

 namely the formation of formic acid when histidine is decomposed by 

 histidase, has been studied more completely by the use of isotopes. It was 

 shown by Soucy and Bouthillier-"' that heavily-labeled serine resulted 

 when histidine-2-C^Mmidazole was fed to rats. Moreover, radioactive 

 allantoin, uric acid, and choline were found to be synthesized in rats after 

 histidine-2-C''' was metabolized. 2"- Carbon-f of histidine has been found 



1^* H. R. V. Arnstein and A. Neuberger, Biochem. J., 48, ii-iii (1951). 

 "" H. R. V. Arnstein and A. Neuberger, Biochem. J., 50, xxxviii (1952). 

 1" H. R. V. Arnstein, Biochetn. J., 48, 27-32 (1951). 

 "8 J. W. Dubnoff, Federation Proc, 9, 1G6 (1950); 10, 178 (1951). 

 139 J. W. Dubnoff, Arch. Biochem., 27, 466-467(1950). 



20° D. Elwyn, A. Weissbach, and D. B. Sprinson, J. Am. Chem. Soc, 73, 5509-5510 

 (1951). 



201 R. Soucy and L. P. Bouthillier, Rev. can. hiol., 10, 290-291 (1951). 



2»2 J. C. Reid and M. O. Landefeld, Arch. Biochem. Biophys., 34, 219-221 (1951). 



