VOL. 12 (1953) LABILE METHYL NEOGENESIS 89 



animals on a methyl-free diet. Both groups of animals received B^g and folic acid in 

 sufficient amounts to ensure synthesis of labile methyl groups and promote growth 

 when the labile methyl groups were not present in the diet. 



The results fitted in with what would be predicted on the basis of the concept 

 outlined. In the case of the animals on the methyl-containing diets, from 5.5 to 10.4% 

 of the choline methyl was derived from the body water, whereas in the case of the 

 animals on the methyl-free diet, the percentages ranged from 24.4 to 34.3. Thus the 

 incorporation of deuterium into the methyl group of chohne in the animals on the 

 methyl-free diet was almost four times as great as that in the animals receiving diets 

 containing labile methyl compounds. 



EXPERIMENTAL 



The eight rats used for these experiments were kept in raised cages equipped for 

 urine collection. Drinking water was made continuously available. The animals were 

 placed on an amino acid diet containing homocystine and choline, but no methionine. 

 The composition of this diet, which was fed ad libitum, is shown in Table I. The weights 



TABLE I 



PERCENTAGE COMPOSITION OF INITIAL DIET 



Sucrose 73 

 Salt mixture^" 4 



Amino acid mixture* 17.2 

 Water soluble vitaminst§ 1 



Corn oil 2 



Vitamins E and K in corn oil** i 



Vitamins A and D cone.*** 0.5 drop 



DL-Homocystine i 



Choline chloride 0.8 



* Glycine, o.i; L-hydroxyproline, o.i; L-proline, 0.2; DL-serine, 0.2; L-aspartic acid, 0.2; dl- 

 alanine, 0.4; L-tryptophan, 0.4; L-arginine • HCl, 0.6; L-histidine-HCl-HjO, 0.7; L-tyrosine, i.o; 

 DL-threonine, 1.4; DL-phenylalanine, 1.5; DL-fsoleucine, 1.8; DL-valine, 2.0; L-glutamic acid, 2.0; 

 L-leucine, 1.3; L-lysine-HCl, 1.9; sodium bicarbonate, 1.4. 



t Biotin, o.oi mg; folic acid, 0.1 mg (increased to 0.4 mg in the case of Rats 30, 31); thiamin 

 chloride, riboflavin, pyridoxine hydrochloride, nicotinic acid, and ^-aminobenzoic acid, i mg each; 

 calcium d-pantothenate, 5 mg; inositol, 10 mg; Vitamin B^g, -^o /ig (except for Rats 30 and 31, which 

 received 15 /ig) ; sucrose to make i g. 



§ In the case of Rats 30 and 31, the vitamins were removed from the diet on the 20th day and 

 the following vitamin solution was given per os in two 0.5 ml portions daily (mg per ml of solution) : 

 thiamin chloride, riboflavin, nicotinic acid, pyridoxine hydrochloride, /3-aminobenzoic acid, 0.8 each; 

 calcium (^-pantothenate, 0.40; inositol, 0.80; folic acid, 0.008; biotin, 0.0008, sucrose, 100 mg. 



** Containing 4 mg of a-tocopherol acetate and 0.1 mg of 2-methyl-i,4-naphthoquinone. 



*** Containing 750 I.U. of vitamin A and 125 I.U. of vitamin D. 



of the animals at various stages of the experiment are summarized in Table II, along with 

 the days on which the dietary regimens were changed. Four of the rats (30, 31, 40 and 

 41) were maintained on a labile methyl-free diet throughout the experimental period. 

 Two of the animals (42 and 43) received the diet given in Table I containing chohne 

 and the other two (44 and 45) received a diet in which the choline was replaced by a i % 

 level of methionine. After the animals had grown on these regimens for the times 



References p. gi. 



