Protein Synthesis in Frog Embryos and Frog Liver Preparations,and Its Inhibition by Embryo Components ∗

Abstract

Summary

The capacity to carry out activities related to protein synthesis has been studied in developing frog embryos and post hatching larvae. Rapid incorporation of labeled amino acids from the external medium into protein could be demonstrated with intact larvae about 5 days before a net increase of total protein was found. Only minor incorporation of labeled amino acid into protein was obtained with cell-free preparations from frog embryos and larvae, even at developmental stages when the total protein content was increasing; however, these preparations did possess a high capacity for amino acid activation. In contrast, analogous cell-free fractions from adult frog liver contained an active system for incorporation of phenylalanine or of an amino acid mixture into protein; the characteristics of the frog liver system were similar to those of cell-free systems for amino acid incorporation described in other species. The low incorporating activity of cell-free preparations from frog embryos or larvae was related to the presence of a soluble, heat-labile component of high molecular weight that strongly inhibited amino acid incorporation by the cell-free system from frog liver. The concentration of this inhibitor in preparations from developing larvae decreased markedly at a developmental stage shortly before the larvae first showed a significant increase of total protein content.