Cytosolic Ca2+-dependent neutral proteinases from rabbit liver: activation of the proenzymes by Ca2+ and substrate.
Two neutral Ca2+-dependent proteinases, differing in molecular size, have been isolated from rabbit liver. Both are recovered as inactive proenzymes that can be converted to the active forms by high (0.1-1.0 mM) concentrations of Ca2+ in the absence of substrate or, in the presence of a protein substrate, by low (1-5 microM) concentrations of Ca2+. The activated proteinases required only 1-5 microM Ca2+ for maximal activity. Substrates hydrolyzed were denatured globin, globin, casein, and to a lesser extent, several extracellular proteins; no digestion was observed with several intracellular cytosolic enzymes tested. Only those proteins that served as substrates were capable of promoting conversion of the proenzymes to the active low-Ca2+-requiring proteinases.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002154:Calpain; D010450:Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D011817:Rabbits; D013379:Substrate Specificity
D004792:Enzyme Precursors; D010450:Endopeptidases; D002154:Calpain; D002118:Calcium