Studies on the phosphomannose isomerase of Amorphophallus konjac C. Koch II. Effect of divalent metal ions on the EDTA-treated enzyme |
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Authors: | Murata Takao |
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Institution: | Department of Physiolosy and Genetics, National Institute of Agricultural Sciences Kitamoto, Saitama 364, Japan |
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Abstract: | Konjak phosphomannose isomerase was inactivated in a time-dependentprocess by metal binding agents, and the inactivated enzymewas instantaneously reactivated by adding such metal ions asZn++, Co++, Fe++, Mn++ and Cu++. However, neither Ca++ nor Mg++were effective for reactivation. Zn++, at a low concentration,brought about complete reactivation of the enzyme at pH 67. The EDTA-treated enzyme was more susceptible to heat denaturationwhen compared with the native enzyme, but the addition of variousmetal ions caused the recovery of the thermal stability of theEDTA-treated enzyme. The magnitude of the recovery dependedon the metal ion species and the concentrations. The most effectivemetal ion was Co++, which caused the recovery of thermal stabilityto a level higher than that of the native enzyme. Phosphomannoseisomerase was inhibited by pchloromercuribenzoate and HgCl2;the inhibition by p-chloromercuribenzoate being more pronouncedas incubation progressed. In contrast, the EDTA-treated enzymewas more readily inhibited by the mercurial ion than was thenative enzyme. Zn++, when added to the EDTA-treated enzyme,markedly restored its resistance to the mercurial-induced inhibition.The metal-substituted enzyme was also inhibited by EDTA in atime-dependent process.
1 This paper constitutes part 4 of studies on konjak mannanbiosynthesis. (Received March 3, 1975; ) |
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