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  • Title: [Endogenous phosphorylation of sarcoplasmic reticulum fragments of rabbit fast skeletal muscles].
    Author: Kurskiĭ MD, Kondratiuk TP, Osipenko AA, Fedorov AN, Grigor'eva VA.
    Journal: Biokhimiia; 1982 Jan; 47(1):34-42. PubMed ID: 6279180.
    Abstract:
    The purified membrane fragments of sarcoplasmic reticulum (SR) of rabbit fast skeletal muscles were found to incorporate 32P from[gamma-32P]ATP in endogenous membrane substrates and in histone H1. The existence of membrane-bound protein kinase of SR was demonstrated by steady state binding of [3H]-cAMP to the SR membranes. The constant of [3H]cAMP binding to the membranes is 2.5 +/- 0.003 x 10(6) M-1, the number of binding sites is 6.1 +/- 0.8 pmol per 1 mg of protein. The endogenous phosphorylation of SR components was inhibited by cAMP and cGMP at concentrations of 10(-7)-10(-6) and depended on Mg2+ and Ca2+. The thermostable protein inhibitor of cAMP-dependent protein kinase inhibited the endogenous phosphorylation of SR membranes by 30-40%. The protein phosphoproduct of SR membranes revealed the properties of a phosphoester. The membrane-bound protein kinase was active towards the exogenous substrate--histone H1. Phosphorylation in the presence of histones was independent of cyclic nucleotides, Mg2+ and Ca2+. Fractionation of 32P-labelled solubilized membranes in polyacrylamide gel in the presence of Na-SDS showed that the radioactivity is bound to protein zones with molecular weights of 95 000 and 6000.
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