The Study of NAD-Malatedehydrogenase in Cytosolic And Mitochondrial Fractions of Amaranth Leaves Under Drought

Localization, isoenzyme spectrum, some physicochemical and kinetic properties of NAD-malate dehydrogenase (L-malate-NAD-oxidoreductaseNAD-MDH, EC 1.1.1.37) have been studied in cytosolic and mitochondrial fractions of mesophyll (M) and bundle sheath cells (BSC) of amaranth leaves during the flowering and grain ripening phases under drought. Depending on the growth phase and tissue type NADMDH has a wide isoenzyme spectrum and pronounced alterations were observed in the isoenzyme number and the enzyme activity and also in physicochemical and kinetic properties. Vmax OAA for cytoplasmic NAD-MDH (sNAD-MDH) was 2 times more than that of mitochondrial NAD-MDH (mNAD-MDH). All isoforms of the enzyme have a wide pH optimum and are temperature tolerant. Depending on the subcellular fraction the enzyme is highly sensitive to OAA and manifests low sensitivity to malate. The reaction catalyzed by NAD-MDH generally follows Michaelis-Menten kinetics and the enzyme is not allosteric. The enzyme activity is strongly regulated by intermediate substrates and divalent ions.