Stimulation by adenosine 3',5'-cyclic monophosphate of protein synthesis by adenohypophyseal polyribosomes

Abstract

Addition of dibutyryl 3',5'-cyclic AMP to slices of bovine pituitary stimulated incorporation of [³H]leucine into protein, whether or not actinomycin D was present; therefore the influence of 3',5'-cyclic AMP on protein synthesis by bovine pituitary polysomes was studied. If the cyclic nucleotide was added to the complete protein-synthesizing system (including pH 5.0 enzyme), stimulation of [³H]leucine incorporation occurred only with pH 5.0 enzyme from rat liver; there was no stimulation when homologous enzyme, i.e., from bovine pituitary, was used. Addition of 3',5'-cyclic AMP to the polysomes, before addition of pH 5.0 enzyme, resulted in stimulation of protein synthesis with either source of enzyme, but stimulation was facilitated to a greater degree, over the range 0.5-2 mM 3',5'-cyclic AMP, when rat liver was the source. The stimulation of protein synthesis was prevented by the addition of cycloheximide. With rat liver pH 5.0 enzyme the product of hydrolysis of 3',5'-cyclic AMP was mainly 5'-AMP whereas with pituitary pH 5.0 enzyme there was also dephosphorylation and deamination resulting in production of hypoxanthine and other bases. However, using either source of pH 5.0 enzyme and the complete protein-synthesizing system (i.e., including an ATP-regenerating mechanism) most of the 3H from hydrolysis of [³H]3',5'-cyclic AMP was incorporated into ATP. The data are seen as compatible with a stimulation by 3',5'-cyclic AMP of translation by pituitary polysomes; the significance of the importance of the source of pH 5.0 enzyme used in the system is obscure.