DECREASE IN CALCIUM-TRANSPORT ASSOCIATED WITH PHOSPHOPROTEIN PHOSPHATASE-CATALYZED DEPHOSPHORYLATION OF CARDIAC SARCOPLASMIC-RETICULUM

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 3  (1) , 45-53
Abstract
Phosphoprotein phosphatase activity is found in preparations of sarcoplasmic reticulum isolated from dog heart when assayed with either histone phosphate or phosphorylated sarcoplasmic reticulum as substrate. Phosphoprotein phosphatase-catalyzed dephosphorylation of the 22,000 dalton phosphoprotein of cardiac sarcoplasmic reticulum is stimulated markedly by MnCl2 (5 mM) and to a lesser extent by MgCl2 (5 mM); Pi (50 mM) and NaF (25 mM) are inhibitory. Dephosphorylation of this 22,000 dalton phosphoprotein is correlated with a decreased initial rate of Ca transport. The close structural and functional relationship of phosphoprotein phosphatase to the cardiac sarcoplasmic reticulum suggests a possible role of this enzyme in reversing the relaxation-promoting effects of catecholamines on the intact heart.