title: A sarcolemma-associated inhibitor is capable of modulating calcium-dependent proteinase activity.
abstract: Purified bovine myocardial sarcolemma vesicles were shown to contain calcium-dependent proteinase inhibitor protein by direct assay and by immunoblot analysis following gel electrophoresis (Western blotting). Calcium-dependent proteinase (calpain, EC 3.4.22.17) was not detected in the sarcolemma vesicles. The inhibitor protein was not solubilized when the vesicles were ruptured by repetitive freezing and thawing. However, a large amount of latent inhibitor activity was exposed after freezing and thawing the sarcolemma, and the inhibitor was much more susceptible to removal by 1.0 M NaCl or proteolysis following this treatment. Since the vesicles were predominantly right-side-out, the latter observations suggested that the inhibitor was associated with the cytoplasmic face of the sarcolemma. The endogenous inhibitor was capable of protecting sarcolemmal protein kinase C from proteolytic conversion to soluble protein kinase M by type I or type II calcium-dependent proteinase. Thus, the inhibitor is probably important in controlling calcium-dependent proteolysis of sarcolemmal proteins.
authors.affiliation: Department of Pharmacology and Therapeutics, Medical College of Ohio, Toledo 43699.
authors.forename: R L
authors.initials: RL
authors.lastname: Mellgren
authors.forename: R D
authors.initials: RD
authors.lastname: Lane
authors.forename: S S
authors.initials: SS
authors.lastname: Kakar
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D002417:Cattle; D002458:Cell Fractionation / Q000379:methods; D005615:Freezing; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology*; D012508:Sarcolemma / Q000502:physiology* / Q000648:ultrastructure; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D002154:Calpain; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase