コイの骨格筋カテプシンAの酵素的諸性質

概要

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Some enzymatic properties of the highly purifted cathepsin A from white muscle of carp were examined. The optimal pH of the cathepsin A was 4.6 in 0.2M acetate buffer solution. Approximate Km values of the cathepsin A for carbobenzoxy (CBZ)-Glu-Phe, CBZ-Glu-Tyr and CBZ-Gly-Phe were 0.42, 0.75 and 14 mM, respectively, in 0.2M acetate buffer solution, pH 5.0. Acetyl-Phe-Tyr (I2) was hardly hydrolyzed by the enzyme. The thermostability of the enzyme was increased in the presence of NaCl and sucrose. Hg2+, pCMB and diisopropyl fluorophosphates were inhibitory on the enzymatic activity. The inhibition of the enzyme by antipan was competitive foe CBZ-Glu-Tyr, with Ki value of 17 μM. The enzymatic activity was inhibited by all the thiol compounds tested at high concentrations. Some discussions were presented as to whether carp cathepsin A and catheptic carboxypeptidase among cathepsins are the same enzyme or not. In the enzyme assay, the fluorometric method using fluorescamine showed some advantages to the conventional ninnhydrin method in simplicity, rapidity, and sensitivity.
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