Studies on the influence of tryptophan and related compounds on hepatic polyribosomes and protein synthesis in the rat.

The effect of the administration of L-tryptophan or tryptophan-related compounds on rat liver RNA and protein metabolism was investigated. The five biochemical parameters studied were polyribosomal aggregation, protein synthesis in vitro, synthesis of cytoplasmic poly(A)-mRNA, release of labeled nuclear RNA in vitro (nuclear and cell sap effects) and nuclear envelope nucleoside triphosphatase activity. The administration of L-tryptophan to overnight fasted rats revealed a rapid stimulation in all of the five parameters. Also, some of the tryptophan-related compounds, especially 5-hydroxy-DL-tryptophan, 3-indolepyruvic acid, indole or 3-hydroxyanthranilic acid, revealed stimulation in many of the parameters. However, when rats were pretreated with puromycin to inhibit protein synthesis, only the administration of L-tryptophan was still able to stimulate significantly the hepatic polyribosomes, in vitro protein synthesis, in vitro nuclear RNA release (involving nuclei but not cell sap) and nuclear envelope nucleoside triphosphatase activity. The effects by the other tryptophan-related compounds became inhibited. The results emphasize the unique action of L-tryptophan on hepatic protein synthesis.