Effects of the α-Hydroxy Analogues of Isoleucine, Lysine, Threonine and Tryptophan and the α-Keto Analogue of Tryptophan and the Level of the Corresponding Amino Acids on Growth of Rats

Abstract

The utilization of the α-hydroxy analogues of isoleucine, lysine, threonine and tryptophan and the α-keto analogue of tryptophan for growth was studied in male weanling rats fed purified amino acid diets. The amino acid mixtures used were those of Rechcigl et al. (10) and Sauberlich (11). The analogues were added to the diet at the expense of the corresponding amino acid. Rats fed the α-hydroxy analogue of isoleucine and the α-keto analogue of tryptophan gained less weight than those fed the corresponding amino acid at the same level. The use of tail cups to prevent coprophagy in one experiment had no apparent effect on utilization of the analogues. The α-hydroxy analogue of tryptophan was equal to tryptophan in promoting growth, whereas the α-hydroxy analogue of lysine and of threonine (prepared with either KMnO₄ or H₂O₂-OsO₄) resulted in weight loss. The levels of isoleucine, lysine, threonine and tryptophan in the complete amino acid mixture were shown to be greater than necessary for maximal body weight gain with the diet used. Rats fed the tryptophan-free diet were hyperexcitable and had convulsions, symptoms unlike those observed during deprivation of other amino acids. Casein was superior to either of the complete amino acid mixtures in promoting weight gain, feed consumption and gain per unit of feed.