Isolation and Characterization of Pyrophosphate : _D-Fructose-6-phosphate 1-Phosphotransferase from Cucumber Seeds

概要

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Pyrophosphate:D-fructose-6-phosphate 1-phosphotransferase was purified over 700-fold from germinating cucumber (Cucumis sativus cv. Fletcher) seeds. The purified enzyme has a specific activity of 5.2 μmol・min^<-1>・mg protein^<-1> in the presence of 1 μM fru-2,6-P_2. The pH optima is similar for both the forward and reverse reactions (pH 7.5-7.8). Magnesium, manganese and cobalt activate the enzyme, with the highest affinity being for magnesium. The enzyme exhibits normal Michaelis-Menten kinetics in both the presence and absence of fru-2,6-P_2. Half-maximum activation of the enzyme was obtained with 35 nM fru-2,6-P_2. Fru-2,6-P_2 stimulates activity by increasing V_<max> and increasing the affinity for fru-6-P, fru-1,6-P_2 and PPi. Phosphate causes non-competitive inhibition with respect to both fru-6-P and PPi. On the basis of the steady-state substrate interaction and Pi inhibition data a sequential ternary complex mechanism is proposed.
日本植物生理学会の論文