Studies on the phosphomannose isomerase of Amorphophallus konjac C. Koch I. Its isolation and some enzymic properties1

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Abstract
A method is described for isolating phosphomannose isomerase from young konjak corms. The enzyme is believed to catalyze the mannose forming reaction in growing corm tissues. The purified enzyme preparation was free from phosphoglucose isomerase activity, and was stable at pH 6–9. Maximum enzyme activity was observed at pH 6.5–7.0. The molecular weight of the enzyme was estimated as 45,000 using Sephadex gel filtration. The following kinetic parameters were obtained: Km (mannose-6-P), 0.73 mM, Keq (fructose-6-P/mannose-6-P), 1.06 at pH 6.5, and activation energy, 11,600 cal/mole. The enzyme was inhibited by the metal binding agents EDTA, o-phenanthroline, and a,a′-bipyridyl. The inhibitory effect of these agents was markedly influenced by the pH level of the incubation mixture, being more pronounced at pH 6 than at pH 8.