title: A calcium-protease activator associated with brain microsomal-insoluble elements.
abstract: A factor which markedly activates Ca2+-dependent thiol protease (calpain) is associated with Triton X-100-insoluble materials, presumably structural elements such as cytoskeletons, of bovine brain microsomal fraction. This factor is extracted with 0.6 M KC1, and purified partially by sucrose density gradient centrifugation and hydroxyapatite column chromatography. The factor appears to be a heat-stable protein with an approximate Mr of 15 000. With casein as substrate this factor activates both calpain I and calpain II several-fold up to more than 10- fold without alteration of their affinity to Ca2+. Calmodulin is unable to substitute for this factor. A similar factor is associated with human platelet insoluble materials.
mesh_terms: D000818:Animals; D001923:Brain Chemistry; D002154:Calpain / Q000378:metabolism*; D002364:Caseins / Q000378:metabolism; D002417:Cattle; D002499:Centrifugation, Density Gradient; D004789:Enzyme Activation; D006868:Hydrolysis; D008861:Microsomes / Q000032:analysis*; D011506:Proteins / Q000302:isolation & purification*; D012995:Solubility
chemical_list: D002364:Caseins; D011506:Proteins; D002154:Calpain