FUNCTION 



deficient in methionine and choline. ^ Choline was isolated from the 

 carcases as the chloroplatinate, and creatine as the creatinine zinc 

 chloride complex. Prolonged feeding of deuterio-methionine yielded 

 choline and creatine containing 85 % of the theoretical deuterium 

 contents. Oxidation of the choline with permanganate yielded tri- 

 methylamine containing all the deuterium originally present in the 

 choline, thus proving that the deuterium had been retained in the 

 methyl groups. 



In a similar experiment deuterio-choline was fed to animals on a 

 methionine- and choline-free diet containing homocystine. Creatine 

 isolated from the body tissues contained 24 to 29 % of the theoretical 

 maximum proving that under certain conditions choline can function 

 as a methyl donator. Aminoethanol was shown « to be the methyl 

 acceptor in the formation of choline, since the administration of 

 aminoethanol containing N^^ led to the formation of choline containing 

 W^. Similarly, guanidinoacetic acid was shown '» « to be the precursor 

 of the amidine and glycine moieties of creatine by the use of com- 

 pounds containing N^^ These experiments indicate that the following 

 transformations can be effected in the rat : 



NH2 . CH3 . CH.OH + 3CH3S . (CH,), . CH . COOH > {CH,),-^ . CH, . CH.OH 



V -M-TT 



^,^ >C . NH . CH, . COOH + CH3S . (CH,), . CH . COOH > V • N . CH, . COOH 



^^2 I NH,/ I 



NH, CH3 



NH. 



xTT:r y • ^H • CH2 . COOH + (CH3)3N . CH, . CH,OH + HS . (CH,), . CH . COOH > 



JNH,/ I 



NH, 



NH 



>C . N . CH, . CH2OH 

 NH,/ I 



CH3 



In this last reaction, homocystine and choline constituted a more 

 effective methylating system for guanidinoacetic acid than did homo- 

 cysteine and choline, suggesting that homocystine may be the carrier 

 of methyl groups in vivo.^ 



When deuterio-creatinine was fed to rats and then ordinary 

 methionine, the rate at which deuterium disappeared from the urinary 

 creatinine was not affected by the level of methionine in the diet, 

 showing that the rate of methyl transfer from methionine was not 

 proportional to the methionine intake.^o 



A deficiency of choline cannot entirely be made good by the 

 administration of methionine, nor can a deficiency of methionine be 



599 



