Amino-acid synthesis in the organism of the white rat

Abstract

It is generally conceded that the organism of the white rat must be supplied with an adequate amount of lysine if normal growth is to result. The purpose of the present series of experiments was to determine whether α-aminocaproic acid (norleucine), which has been shown to be present in the proteins of the central nervous system, could replace lysine in the diet. No evidence exists that in the young rat aminization of fatty acids with the resulting formation of aminoacids takes place. It was considered that it might be possible to introduce a second amino group into the caproic acid molecule provided one amino group was already present in the α position. In view of the current idea as to the probable position of the ∊ amino group of lysine in the protein molecule, the possibility also suggested itself that synthesis of a protein without the free amino group of lysine might occur by substitution of norleucine for lysine in the molecule.

Young white rats were fed diets containing 18 per cent. gliadin (wheat), lard, purified butter fat, starch, and protein-free milk. Maintenance or slow growth was observed. That this failure of normal growth was due to protein deficiency was demonstrated by normal growth of young rats on a similar diet in which casein replaced gliadin. Substitution of 0.5 and 1.5 per cents. of norleucine for equivalent amounts of gliadin did not alter the rate of growth. Normal growth occurred, however, when I per cent. lysine replaced an equivalent amount of gliadin or was substituted for the norleucine. These results are in agreement with those of Osborne and Mendel in demonstrating the efficiency of lysine as a supplement to a gliadin diet.