Kinin inactivating enzyme from mushroom Tricholoma conglobatum. II. Some enzymatic properties of the purified enzyme.

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Some enzymatic properties of the new potent kinin inactivating enzyme (named as Shimeji kininase) which was purified from a mushroom Tricholoma conglobatum (Shimeji, in Japanese) were studied. This enzyme inactivated bradykinin, kallidin and Met-Lys-bradykinin by the ratio of 1.0 : 1.0 : 1.5, respectively, calculated as the molar ratio, and its Km value for bradykinin hydrolysis was 1.9 μM. Isoelectric point and molecular weight of the enzyme were 4.5 and 6.6×104, respectively. Optimum pH of this enzyme was 7.4 and it was comparatively stable at pH 6-9. This enzyme was thermolabile, i.e., more than 50% of the activity vanished by heating at 45° for 10 min and completely vanished at 60° for 10 min. The chelating agents, trasylol, SBTI and bradykinin potentiator B had no detectable influence upon the kininase activity of the enzyme. TLCK, TPCK and DFP weakly inhibited the enzymatic activity. The mercurials strongly inhibited the enzymatic activity of it and the inhibited activity was restored by adding excess amount of 2-mercaptoethanol. Accordingly, sulfhydryl groups in the enzyme molecule are requisite for its kininase activity and this enzyme may be classified as the thiol enzyme. The enzyme hydrolyzed the amino terminal substituted peptides such as Bz- and Z-derivatives while N-terminal free di- or tri-peptides were hardly hydrolyzed by it.

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