Metabolism of N-Alkyl Derivatives of Amino Acids

The metabolism of certain N-alkyl derivatives of phenylalanine, valine, leucine, and isoleucine has been studied by the methods of Rose and coworkers. 1 Young white rats were fed an adequate diet containing carbohydrate, fat, inorganic salts, vitamins, and a mixture of purified amino acids. In the diets of the experimental animals the amino acid being studied was replaced by varying amounts of the corresponding N-alkyl derivatives. The growth of the rats was followed over a 28-day period.

The results of these studies are shown in Table I.

These data and the results of other investigators with the N-alkyl derivatives of histidine, 2 tryptophane, 3 , 4 , 5 methionine, 6 lysine, 7 and cystine 8 may be summarized as follows:

1. The N-methyl derivatives of the d- forms of the essential amino acids are not utilized by the white rat for growth purposes.

2. With the exception of cystine the N-methyl derivative of the l- form of the amino acid has the same nutritive value as the corresponding unmethylated d- form. Thus both the d- form 1 and the N-methyl derivative of the l- form of phenylalanine, methionine, tryptophane, and histidine support growth; while the d- form, 1 and the N-methyl derivative of the l- form of lysine, valine, leucine, and isoleucine fail to do so. It is interesting to note that whereas the N-methyl derivative of l-phenylalanine is utilized by the rat neither the N-ethyl nor the N, N-dimethyl derivative supports growth.