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Day DA, Neuburger M, Douce R, Wiskich JT: Exogenous NAD Effects on Plant Mitochondria: A Reinvestigation of the Transhydrogenase Hypothesis. Plant Physiol. 1983 Dec;73(4):1024-1027.
Addition of NAD (+) to purified potato (Solanum tuberosum L.) mitochondria respiring alpha-ketoglutarate and malate in the presence of the electron transport inhibitor rotenone, stimulated O (2) uptake. This stimulation was prevented by incubating mitochondria with N-4-azido-2-nitrophenyl-aminobutyryl-NAD (+) (NAP (4)-NAD (+)), an inhibitor of NAD (+) uptake, but not by 1 mm EGTA, an inhibitor of external NADH oxidation. NAD (+)-stimulated malate-cytochrome c reductase activity, and reduction of added NAD (+) by intact mitochondria, could be duplicated by rupturing the mitochondria and adding a small quantity to the cuvette. The extent of external NAD (+) reduction was correlated with the amount of extra mitochondrial malate dehydrogenase present. Malate oxidation by potato mitochondria depleted of endogenous NAD (+) by storing on ice for 72 hours, was completely dependent on added NAD (+), and the effect of NAD (+) on these mitochondria was prevented by incubating them with NAP (4)-NAD (+). External NAD (+) reduction by these mitochondria was not affected by NAP (4)-NAD (+). We conclude that all effects of exogenous NAD (+) on plant mitochondrial respiration can be attributed to net uptake of the NAD (+) into the matrix space. |
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