656 VI. OCCUERENCE OF LIPIDS IN THE ANIMAL 



conversion of formate to the labile methyl group obtains after the sub- 

 cutaneous administration of sodium deuterio-C 14 -formate to rats. Formic 

 acid is able to give rise to methyl, not only when it is present as the sodium 

 salt, but also when it is administered as an ester such as formyl-L-phenyl- 

 alanine. 695 



Methanol is another one-carbon compound which can be changed to a 

 labile methyl group. Positive results were obtained not only by Arnstein 662 

 but also by the du Vigneaud group. 695,698 Formaldehyde has likewise been 

 found to be a precursor of the methyl radicle. 694 - 695 However, the C of 

 sodium bicarbonate 694 cannot serve as a source of the methyl group. 

 Moreover, C0 2 arising from oxidation of D-/3-C 1 "-serine or the — C 14 OOH 

 of glycine cannot be transformed to — CH 3 . 662 



Arnstein, 662 and Jansson and Mosher 663 proved that the a-carbon atom of 

 glycine and the /3-carbon of L-serine both appear in the labile methyl frac- 

 tion. Toporek, Miller, and Bale 699 have also reported that the L-histidine 

 may contribute the number 2 carbon of its molecule to the labile methyl 

 groups of the liver, blood, and body choline, as well as of the body creatine. 

 These workers showed that, when a choline deficiency existed, the synthesis 

 was accelerated both in vivo and in vitro. When additional amino acids 

 (both essential and non-essential) were given to rats, the conversion of the 

 histidine carbon 2 to methyl was retarded. It is suggested that other 

 sources of synthesis of methyl are now available, so that those arising from 

 histidine are not so critically required, although they are an important 

 dietary source. 



Du Vigneaud and associates 700 reported that the synthesis of small 

 amounts of methyl continues to occur in the tissues even when the diet con- 

 tains an adequate amount of preformed methyl groups. There is no dis- 

 tinction between the direct synthesis of choline in the tissues and synthesis 

 by intestinal bacteria, with the subsequent utilization of such newly formed 

 methyl groups in the tissues. However, the bacteria are not required either 

 primarily or secondarily for the synthesis of labile methyl. 



Although bacteria are not necessary for the synthesis of the labile methyl 

 radicle, animals which could utilize homocystine for growth on a methyl- 

 free diet lost this ability after receiving the diet plus 2% sulfasuxidine over 

 a five-month period. The capacity to utilize homocystine for growth was 

 restored after the animals were put back on the preexperimental diet. 



698 V. du Vigneaud and W. G. Verly, /. Am. Chem. Soc, 72, 1049 (1950). 



699 M. Toporek, L. L. Miller, and W. F. Bale, J. Biol. Chem., 198, 839-851 (1952). 



700 V. du Vigneaud, S. Simmonds, J. P. Chandler, and M. Cohn, /. Biol. Chem., 159, 

 755-756 (1945). 



