288 VI. ACETIC, FORMIC, AND PROPIONIC ACIDS 



greatly exceeded that of the choHne methyl groups; this suggests that most 

 of the newly-synthesized methyl groups are first incorporated into me- 

 thionine and are then transferred to choline by transmethylation. Cobala- 

 min (B]2, or "animal protein factor") was isolated in 1948 and was found 

 to be a cobalt coordination compound, or "chelate." A second homol- 

 ogous form was isolated in 1949. These forms were identified as cyano 

 (B12) and hydroxo (B.2* = B12*) forms of the organometallic molecule con- 

 taining cobalt.^'" Cobalamin was found to increase the conversion of /3- 

 C^^-serine, a-C^'^-glycine, and formate into the methyl group of methio- 

 nine and into both the methyl groups and the ethanolamine moiety of 

 choline. 



Little is known about the appearance of formate in animals. Kendal 

 and Ramanathan^'^ reported the appearance of formate in the urine of man 

 after the administration of methanol. AVhen ethanol was ingested, the 

 elimination of formate was completely inhibited in repeated experiments. 

 Formate appeared in the urine within one or two hours after the cessation 

 of ethanol ingestion ; its appearance was coincident with the rapid decline 

 in the body methanol concentration which ensues. 



According to Sperling et a/.,^^^ carbonate and formate have the same 

 general pattern of excretion and distribution after their intraperitoneal 

 injection into rats. More than 90% of the injected dose of C^^-carbonate 

 was excreted in twenty-four hours, while an excess of 80% of C^*-formate 

 was excreted during the same period. The retained C^^ was distributed 

 throughout all the tissues in both groups of animals. 



3. The Metabolism of Propionic Acid 



In contradistinction to the formate and acetate residues, which are 

 transferred and metabolized as units, and which serve as intermediates 

 in the synthesis of many biologically-important compounds, propionic acid 

 does not have a similar metabolic function; the metabolism of propionic 

 acid is closely related to that of the various three-carbon intermediates. 



Propionic acid does not give rise to ketone bodies23.24,36 ^^ ^\^q fasting 

 rat; on the other hand, propionic acid is converted to glycogen both when 

 fed as the sodium salt of the acid^^ and when administered as the ethyl 

 ester. ^2 Moreover, other odd-chain acids are believed to be oxidized to 



''I" P. B. Hawk, B. L. Oser, and W. M. Summerson, Practical Physiological Chemistry, 

 13th ed., Blakiston, New York, Toronto, 1954, pp. 1207 ff. 



211 L. P. Kendal and A. N. Ramanathan, Biochetn. J., 54, 424-426 (1953). 



2'2 F. Sperling, E. S. Maxwell, and W. F. Van Oettingen, Am. J. Physiol, 174, 33-38 

 (1953). 



