Purification and Characterization of an Inhibitor of Calcium- Activated Neutral Protease from Rabbit Skeletal Muscle

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Abstract
An endogenous inhibitor of calcium-activated neutral protease was purified to homogeneity from rabbit skeletal muscle using ion-exchange chromatography on DEAE-cellulose and QAE-Sephadex A-50 columns, chromatofocusing, and hydro phobic interaction chromatography on a phenyl-Sepharose CL-4B column. The purified inhibitor was shown to be a dimer of identical subunits and each subunit has a molecular weight of about 34,000. This inhibitor was remarkably thermo and acid-stable. It was specific for calcium-activated neutral protease and had no effect on any other protease examined (trypsin, papairi, cr-chymotrypsin, bromelain, etc.). It is demonstrated that the inhibition is due to the formation of a stoichio metric complex between two enzyme molecules and one inhibitor molecule.