| Abstrakt: |
NADP+‐malic enzyme (l‐malate: NADP+ oxidoreductase, decarboxylating EC 1.1.1.40) from pod walls of chickpea was purified 51‐fold by ammonium sulphate fractionation, DEAE‐ cellulose chromatography and gel filtration through Sepharose 4B. The purified enzyme required a divalent cation, either Mn2+ or Mg2+, for its activity. Km values at pH 7.8 for malate, NADP+ and Mn2+ were 4.0, 0.031 and 0.71 mM, respectively. Mn2+‐dependent activity was inhibited by heavy metal ions such as Cd2+, Zn2+, Hg2+, and to a lesser extent by Pb2+ and Al3+. Among the organic acids examined, sodium salts of oxalate and oxaloacetate were inhibitory. Kinetics of the reaction mechanism showed sequential binding of malate and NADP+ to the enzyme. Products of reaction, viz. pyruvate, bicarbonate and NADPH, inhibited the enzyme activity. At limiting concentrations of NADP+, pyruvate and bicarbonate induced a positive cooperative effect by malate. It is proposed that the activity of NADP+‐malic enzyme is controlled by intracellular concentrations of substrates and products. [ABSTRACT FROM AUTHOR] |
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