ASPECTS OF CONTROL OF PROTEIN SYNTHESIS IN NORMAL AND REGENERATING RAT LIVER, II. A MICROSOMAL INHIBITOR OF AMINO ACID INCORPORATION WHOSE ACTION IS ANTAGONIZED BY GUANOSINE TRIPHOSPHATE

Abstract

Evidence was presented that normal adult rat liver microsomes contain, in excess over their regenerating liver counterparts, a heat-labile factor(s) that inhibits amino acid incorporation on ribosomes. The factor may be isolated in soluble form by sonic disruption of microsomes. The bulk of its activity sediments in a polydisperse fashion on sucrose gradients. Its action is antagonized by guanosine triphosphate (GTP). It does not function by depleting GTP in the assay system, by destroying messenger, or interfering with its binding. It is suggested that protein synthesis in normal adult tissues may be under control of an inhibitory element(s), and that GTP may play a role in regulatory processes.