Iyer R B, Koritz S B, Kirchberger M A
Department of Biochemistry, Mount Sinai School of Medicine, New York, NY 10029.
Mol Cell Endocrinol. 1988 Jan;55(1):1-6. doi: 10.1016/0303-7207(88)90084-6.
Inhibitor-1 following phosphorylation by protein kinase A inhibits phosphoprotein phosphatase-1. We have found that in the rat heart inhibitor-1 is present only in the cytosolic fraction and that its phosphorylation in ventricular slices was increased by isoproterenol but not by isoproterenol and propranolol together. Cardiac microsomal phosphoprotein phosphatase activity, with added phosphorylase a as the substrate, was inhibited 33% by phosphorylated inhibitor-1. Phosphorylated inhibitor-1 decreased the dephosphorylation by exogenous phosphoprotein phosphatase-1 of phospholamban present in the sarcoplasmic reticulum membranes. These results suggest an interaction of cytoplasmic inhibitor-1 with either cytoplasmic or membrane-bound phosphoprotein phosphatase-1 with a subsequent effect on the level of phosphorylated phospholamban and the probable involvement of this interaction in the cardiac response to beta-adrenergic hormones.
蛋白激酶A磷酸化后的抑制因子-1可抑制磷酸蛋白磷酸酶-1。我们发现，在大鼠心脏中，抑制因子-1仅存在于胞质部分，并且异丙肾上腺素可增加心室切片中其磷酸化水平，但异丙肾上腺素与普萘洛尔共同作用时则不然。以添加的磷酸化酶a为底物时，心脏微粒体磷酸蛋白磷酸酶活性被磷酸化的抑制因子-1抑制了33%。磷酸化的抑制因子-1减少了肌浆网膜中存在的受磷蛋白被外源性磷酸蛋白磷酸酶-1去磷酸化的程度。这些结果表明，细胞质中的抑制因子-1与细胞质或膜结合的磷酸蛋白磷酸酶-1之间存在相互作用，随后会对受磷蛋白的磷酸化水平产生影响，并且这种相互作用可能参与了心脏对β-肾上腺素能激素的反应。
