title: Evidence for non-competitive inhibition between two calcium-dependent activated neutral proteinases and their specific inhibitor.
abstract: Two muscle thiol proteinases causing partial degradation of myofibrillar constituents were isolated and purified from skeletal muscle. The two proteinases that differ significantly in calcium requirements were designated respectively high- and low-Ca2+-requiring proteinase. Both are inhibited, in vitro, by a specific inhibitor which is a protein also isolated from skeletal muscle. Experiments using carboxymethylated monomeric proteinases and inhibitor-conjugated Sepharose were carried out in order to understand the mechanism of control of the proteinases by the inhibitor. The results using increasing inhibitor concentrations show a non-competitive inhibition for both enzymes. The Ki value for the low-Ca2+-requiring form was 0.3 microM, while the Ki value for the high-Ca2+-requiring form was 0.9 microM. Likewise, the low-Ca2+-requiring form needs about 3-fold more inhibitor than the high-Ca2+-requiring form for the same per cent inhibition.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003546:Cysteine Endopeptidases; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D009132:Muscles / Q000201:enzymology*; D011480:Protease Inhibitors / Q000302:isolation & purification*; D011485:Protein Binding; D011817:Rabbits
chemical_list: D007527:Isoenzymes; D011480:Protease Inhibitors; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002118:Calcium