Nuclear metabolism. II protein synthesis by isolated calf thymus nuclei

Abstract

Isolated nuclei from calf thymus gland actively incorporate [ 14C]-amino acids into the nuclear proteins. The energy for protein synthesis in the isolated nuclei is derived from both glycolysis and oxidative phosphorylation. Our results suggest that 2,4-dinitrophenol inhibition of protein synthesis not only occurs because it is an uncoupler of nuclear oxidative phosphorylation, but it may also inhibit the “transport” of necessary constituents in the incubation mixture to the intranuclear sites of synthesis. Amino acid incorporation by the isolated nuclei into protein responded differently to some of the inhibitors of nuclear phosphorylation phorylation such as malonate and maleate. Cytidine and guanosine, which were reported to inhibit nuclear phosphorylation (9), can bring about a substantial stimulatory effect on nuclear protein synthesis especially when ribose-5-phosphate is added to the incubation mixture. Fructose-1,6-diphosphate, on the other hand, stimulated nuclear phosphorylation (9), but caused 50% inhibition of nuclear protein synthesis. The differential effect on nuclear phosphorylation and protein synthesis indicates that the nucleus has different sites or compartments for biochemical activities which are dependent upon or connected with each other and that certain cytoplasmic metabodites can exert a profound effect on the rate and magnitude of various nuclear pathways.