Ca2+ and Phospholipid-Dependent Protein Kinase Activity and Phosphorylation of Endogenous Proteins in Bovine Adrenal Medulla |
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Authors: | Bradley C. Wise Erminio Costa |
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Affiliation: | Laboratory of Preclinical Pharmacology, National Institute of Mental Health, Saint Elizabeths Hospital, Washington, D.C., U.S.A. |
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Abstract: | Abstract: Soluble and membrane fractions of bovine adrenal medulla contain several substrates for the Ca2+/ phospholipid-dependent and cyclic AMP-dependent protein kinases. The phosphorylation of soluble proteins (36 and 17.7 kilodaltons) and a membrane protein (22.5 kilo-daltons) showed an absolute requirement for the presence of both Ca2+ and phosphatidylserine; other substrates showed less stringent phosphorylation requirements and many of these proteins were specific for each of the protein kinases. The Ca2+/phospholipid-dependent phosphorylation was rapid, with effects seen as early as at 30 s of incubation. Measurement of enzyme activities with histone HI as an exogenous substrate demonstrated that the Ca2+/phospholipid-dependent protein kinase was equally distributed between the soluble and membrane fractions whereas the cyclic AMP-dependent enzyme was predominantly membrane-bound in adrenal medulla and chromaffin cells. The activity of the soluble Ca2+/phos-pholipid-dependent protein kinase of adrenal medulla was found to be about 50% of the enzyme level present in rat brain, a tissue previously shown to contain a very high enzyme activity. These results suggest a prominent role for the Ca2+/phospholipid-dependent protein kinase in chromaffin cell function. |
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Keywords: | Phosphorylation Protein kinases Calcium Phospholipid Cyclic nu-cleotides Adrenal medulla |
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