Properties of NADP⁺‐malic enzyme from pod walls of chickpea (<i>Cicer arietinum</i>)

Abstract

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 Mn 2+ or Mg 2+ , for its activity. K m values at pH 7.8 for malate, NADP + and Mn 2+ were 4.0, 0.031 and 0.71 m M , respectively. Mn 2+ ‐dependent activity was inhibited by heavy metal ions such as Cd 2+ , Zn 2+ , Hg 2+ , and to a lesser extent by Pb 2+ and Al 3+ . 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.