The cytosolic mitochondrial forms of NAD-malate dehydrogenase(EC 1.1.1.37), which ware extracted from leaves of Mesembryanthemum crystallnum L. in the CAM mode, were compared with respect to their enzymatic properties. Citrate was a strong inhibitor for the activity of the cytosolic enzyme but a weak one for the activity of the mitochondrial enzyme. The cytosolic enzyme was inhibited by 2-ketoglutarate and pyruvaer more than the mitochondriak enzyme. There were no differences in inhibitions by ATP and ADP between the isozymes. The optimal Ph for the activity of the cytosolic enzyme was over a wide range from 7.0 to 8.5, whereas that for the activity of the vytosolic enzyme was around 8.5 Inorganic phosphate reversed the inhibition of the cytosolic enzyme by citrate partially but not the inhibition by 2-ketogkutarate. Inorganic phosphate reversed the inhibitions of the mitochondrial enzyme by ATP and ADP more than that of the cytosolic enzyme. Inorganic phosphate inhibited the cytosolic enzyme but not the mitochondriak enzyme.
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