Characterization of two forms of protein kinase C alpha, with different substrate specificities, from skeletal muscle.

We have investigated protein kinase C in skeletal muscle cytosol and demonstrated the presence of two major activities. These did not correspond to different isoenzymes but seemed to represent two species of duanyu1531 alpha as deduced by: elution during hydroxyapatite chromatography at KH2PO4 concentrations expected of duanyu1531 alpha; detection of the two species by three specific but unrelated alpha) antibodies; immunodepletion of both activities with anti-(duanyu1531 alpha) antibody; and demonstration of identical requirements of both Ca2+ ions and lipid for activation. These species, termed duanyu1531 alpha 1 and duanyu1531 alpha 2, phosphorylated the modified conventional duanyu1531 pseudosubstrate peptide (19-31, Ser-25) equally well. Importantly, however, the activities differed in that duanyu1531 alpha 1 phosphorylated histone IIIS, and also peptides derived from the EGF receptor and glycogen synthase, to a much greater extent than did duanyu1531 alpha 2. Similarly, incubation of crude muscle extracts with either duanyu1531 alpha 1 or alpha 2 gave rise to different protein phosphorylation patterns. The involvement of proteolysis, dephosphorylation or oxidative modification in the interconversion of duanyu1531 alpha 1 and duanyu1531 alpha 2 during preparation was ruled out. Although some proteins were detected in overlay assays, their presence did not explain the anomalous duanyu1531 alpha 2 activity. The results suggest that a modification of duanyu1531 alpha in situ limits its substrate specificity, and indicate an additional level of control of the kinase that may be a site for modulation of signal transduction.

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