The Mode of Inhibition by Salts to Two Enzymes Involved in IMP Degradation in Fish Flesh

Abstract

In order to clarify the mode of inhibition by salts, some properties of two enzymes involved in IMP degradation during the cold-storage of fish flesh were studied. Crude 5'-nucleotidase from walleye pollack showed an optimum pH of about 8.0 and an apparent Km value of 0.83mM for IMP, while that from silver whiting showed the pH of above 9.0 and the Km value of 0.18mM. They were uncompetitively inhibited by NaCl with the K; values of 0.38 and 0.36M, respectively. CaCl2 and KCl also inhibited their activity. On the other hand, crude purine nucleoside phosphorylase from walleye pollack showed the Km value of 0.20mM for inosine, while that from silver whiting showed the value of 0.1mM. The former was not inhibited by NaCl and CaCl2, but the latter was noncompetitively inhibited by NaCl with the K; value of 1.0M.