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Biochemical analyses of plant mitochondrial NAD(P)H dehydrogenases
Abstract
Plant mitochondria possess the unique ability to oxidize cytosolic reducing equivalents in the form of NADH and NADPH. In this dissertation, the enzymes responsible for exogenous NADH and NADPH oxidation in red beetroot (Beta vulgaris L.) and maize (Zea mays L.) mitochondria were partially purified and characterized. Three NAD(P)H dehydrogenase activities were found in the soluble protein fraction of "aged" red beetroot mitochondria. One of these dehydrogenases was purified to a single polypeptide with an apparent molecular weight of 42 kilodaltons. This dehydrogenase was capable of oxidizing both NADH and NADPH. This enzyme represents greater than 90% of the recoverable NADPH dehydrogenase activity and, therefore, the 42 kilodalton dehydrogenase is likely an exogenous NAD(P)H dehydrogenase. A second dehydrogenase was partially purified to a major polypeptide of 55 kilodaltons and a minor protein of 40 kilodaltons. This dehydrogenase oxidized only NADH, and was sensitive to a potent and specific inhibitor of the exogenous NADH dehydrogenase, platanetin, a dihydroxyflavone isolated from the bud scales of plane (Plantanus accidentalis) trees. A third NADH dehydrogenase was purified from red beetroot mitochondria that specifically oxidized NADH and consisted of a 32 kilodalton protein. All three dehydrogenase activities were insensitive to inhibition by rotenone, a specific inhibitor of the endogenous NADH dehydrogenase (Complex I of the mitochondrial electron transport chain). Two NAD(P)H dehydrogenase activities were partially purified from the soluble protein fraction of maize mitochondria isolated from etiolated seedlings. One of these dehydrogenases oxidized both NADH and NADPH, and represented greater than 70% of the recoverable NADPH dehydrogenase activity, implicating that this enzyme likely represents the exogenous NADH and NADPH dehydrogenase. Furthermore, the NAD(P)H dehydrogenase activities of this enzyme were sensitive to inhibition by the plane tree bud extract containing platanetin. This exogenous NAD(P)H dehydrogenase was partially purified and appears to be comprised of three major polypeptides with apparent molecular weights of 60, 58 and 42 kilodaltons. The maize exogenous NAD(P)H dehydrogenase was found to be immunologically related to the red beetroot 55 kilodalton NADH dehydrogenase.
Subject Area
Biochemistry|Botany
Recommended Citation
Luethy, Michael Hans, "Biochemical analyses of plant mitochondrial NAD(P)H dehydrogenases" (1992). ETD collection for University of Nebraska-Lincoln. AAI9314416.
https://digitalcommons.unl.edu/dissertations/AAI9314416