Effect of tryptophan on polyribosomes and protein synthesis in liver

Abstract

The effect of tryptophan on hepatic polyribosomes and protein synthesis in rats and mice was studied under several experimental conditions. Young rats that had been forcefed for 4 days a purified complete diet containing adequate tryptophan were given l-tryptophan or water by stomach tube 16 hr after the last evening feeding and killed 1 or 2 hr later. The livers of the tryptophan-administered rats revealed a shift toward heavier polyribosomes, and in vitro protein synthesis, using postmitochondrial supernatant or microsomes, was increased. Rats bearing intrahepatically transplanted hepatoma H5l23 were fasted for 3 days and then received tryptophan orally 1 or 2 hr before being killed. Liver, but not hepatoma, tissue showed an increase in in vitro protein synthesis. Mice fasted overnight or rats fasted for 2 days received tryptophan by stomach tube 1 or 2 hr before being killed. Sucrose density gradient patterns of hepatic polyribosomes were studied. Polyribosomes from deoxychol ate-treated postmitochondrial supernatant and free polyribosomes showed a marked shift toward heavier aggregates and a 76% and 46% increase, respectively, in in vitro protein synthesis, whereas membrane-bound polyribosomes showed a moderate shift toward heavier aggregates and a 20% increase in in vitro protein synthesis.