Nuclear protein phosphokinase activities and phosphorylation of chromosomal proteins in embryonic and adult muscles of the chick.

Abstract

Nuclei isolated from chick embryonic (11-days old) and adult muscles contain 25% and 15%, respectively, of the total cellular protein phosphokinase activity. The specific activity, on a DNA basis, of the adult enzyme is approximaely 4 times lower than that of the nuclei from 11-day-embryos. Nuclear extracts of either stage of development give rise on DEAE cellulose chromatography to two main protein kinase activity peaks, which elute at 20mm and 300mm phosphate buffer, pH 7 (protein kinases “A” and “C”, respectively). Nuclei of adult muscles contain 10 fold and 3 fold less protein kinases A and C, respectively, than embryonic nuclei. The properties (substrate specificity, effect on activity of NaCl and phosphate, cyclic AMP activability, molecular weight) of protein kinases A and C are different, but those of embryonic and adult protein kinase A or C are indistinguishable, indicating that the transition from nuclei with an active mitosis (embryonic) to a resting state (adult) is accompanied by a quantitative, but not a qualitative, change in the protein kinase pattern.