Purification and some properties of phosphomannomutase from corms of Amorphophallus konjac C. Koch

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Phosphomannomutase [Glazer et al.: Biochim. Biophys. Acta 33: 522-625 (1959)] was purified 1700-fold in a 39% yield from cell-free extract of konjak (Amorphophallus konjac C. Koch) corms. The molecular weight of the enzyme as determined by gel filtration was about 62,000. The enzyme required both Mg^<2+> and a-D-glucose-1,6-bisphosphate for activity, although Mg^<2+> was partially replaceable by either Co^<2+> or Ni^<2+>. An apparent equilibrium constant, K_<eq>=(mannose-6-phosphate) (mannose-1-phosphate), was determined to be 8.5. Activity was maximal at pH 6.5 to 7.0. Activation energy was 11.1 kcal/mole. The enzyme was the most stable at pH 7.5. The addition of substrate or cofactor markedly increased enzyme stability toward heat denaturation. The enzyme was more labile to heat than phosphoglucomutase from konjak corms. Treatment with various metal ions in Tris buffer inhibited the enzyme. Cu^<2+> and Zn^<2+> were the most potent inhibitors among the metal ions tested, while Co^<2+> and Ni^<2+> were weak. When the enzyme was treated with metal ions in the presence of histidine buffer, Cu^<2+> and Zn^<2+> showed no inhibitory effect on the enzyme, whereas Be^<2+> inhibited it to an extent similar to that in Tris buffer. Plots of 1/v versus 1/(mannose-1-phosphate) at different fixed concentrations of glucose-1,6-bisphosphate and 1/v versus 1/(glucose-1,6-bisphosphate) at different fixed concentrations of mannose-1-phosphate were series of converging lines. Mannose- 1-phosphate at high concentrations was found to inhibit the enzyme competitively with respect to glucose-1,6-bisphosphate. Apparent K_m and K_i values for mannose-1-phosphate were calculated to be 0.2 mM and 1.2 mM, respectively. The K_m value for glucose-1,6-bisphosphate was 1.8 μM.
日本植物生理学会の論文

Purification and some properties of phosphomannomutase from corms of Amorphophallus konjac C. Koch

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