Effect of tryptophan on polyribosomes and protein synthesis in liver

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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.