Rat Growth Experiments with -Phenylserine Diastereoisomers.

Abstract

Though much less toxic than phenylserine, allophenylserine cannot give rise to phenylalanine or tyrosine. Synthetic diets containing 0.7% of either the DL-diastereomer and 0.4% L-phenylalanine (no tyrosine) neither promoted nor repressed growth of young white rats (50-60 g). Considerable loss of weight occurred when 0.7% phenylserine was added to a synthetic diet containing 0.8% L-tyrosine (no phenylalanine), but 0.7% allophenylserine caused little change. Food consumption (ad lib.) was comparable with that of control animals in both instances. The growth of older rats (250-300 g) on lactalbumin diets followed a similar pattern. Addition of 2.0% phenylserine resulted in a considerable loss of weight, in part due to a lower food intake. When 2.0% allophenylserine was added to the diet, growth and food consumption paralleled those of control animals. The toxic effect of phenylserine is probably due to the fact that it is more rapidly metabolized to toxic substances than is allophenylserine, rather than to its greater activity as a competitive antagonist of phenylalanine or tyrosine.