Abstract
Properties of partially purified NADP-malic enzyme (EC 1.1.1.40) from glumes of developing wheat grains were examined. The pH optimum for enzyme activity was influenced by malate and shifted from 7.3 to 7.6 when the concentration of malate was increased from 2 to 10 mM. The K m values, at pH 7.3, for various substrates were: malate, 0.76 mM; NADP, 20 μM and Mn 2+, 0.06 mM. The requirement of Mn 2+ cation for enzyme activity could be partially replaced by Mg 2+ or Co 2+. Mn 2+ dependent enzyme activity was inhibited by Pb 2+, Ni 2+, Hg 2+, Zn 2+, Cd 2+, Al 3+ and Fe 3+. During the reaction, substrate molecules (malate and NADP) reacted with enzyme sequentially. Activity of malic enzyme was inhibited by products of the reaction viz pyruvate, HCO 3 − and NADPH 2. At a limiting fixed concentration of NADP, these products induced a positive cooperative response to increasing concentrations of malate.
Published Version
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