title: Presence in many mammalian tissues of an identical major cytosolic substrate (Mr 100 000) for calmodulin-dependent protein kinase.
abstract: Incubation of cytosol fractions from a variety of mammalian tissues (heart, liver, lung, adrenal, spleen and skeletal muscle) with Ca2+ (0.5 mM) in the presence of gamma-[32P]ATP resulted in the phosphorylation of a prominent substrate of Mr approximately 100 000 (100 kDa). One-dimensional peptide maps and two-dimensional tryptic fingerprints of the phosphoprotein from these sources were identical. A single major phosphopeptide was generated by trypsin and was determined to contain exclusively phosphothreonine. The 100 kDa substrate could be distinguished from glycogen phosphorylase (Mr approximately 97 000) by a number of criteria including phosphopeptide mapping and by its failure to bind either to glycogen or to a specific antiphosphorylase antibody. The Ca2+-dependent protein kinase responsible for phosphorylation of the 100 kDa protein appeared to be a calmodulin (CaM)-requiring enzyme in that it could be inhibited in cytosol extracts by trifluoperazine (IC50 6-16 microM) and that exogenous CaM was necessary for 100 kDa phosphorylation in CaM-depleted cytosol. These results suggest that a rise in intracellular Ca2+ resulting in an activation of CaM-dependent protein kinase leads to the phosphorylation of a common 100 kDa substrate in many tissues.
mesh_terms: D000311:Adrenal Glands / Q000201:enzymology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002417:Cattle; D003600:Cytosol / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D008099:Liver / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D009132:Muscles / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D013154:Spleen / Q000201:enzymology; D013379:Substrate Specificity
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D011494:Protein Kinases; D002118:Calcium