PLATANETIN AND 7-IODO-ACRIDONE-4-CARBOXYLIC ACID ARE NOT SPECIFIC INHIBITORS OF RESPIRATORY NAD(P)H DEHYDROGENASES IN POTATO-TUBER MITOCHONDRIA

Progress in understanding the role of NAD(P)H oxidation in plant respi ration is restricted by the lack of access to specific inhibitors of e ach of the unknown number of NAD(P)H dehydrogenases in the inner mitoc hondrial membrane. Platanetin (3,5,7,8-tetrahydroxy-6-isoprenyl flavon e) is known to be an inhibitor of external NADH oxidation by plant mit ochondria, while 7-iodo-acridone-4-carboxylic acid (IACA) is an inhibi tor of an internal, rotenone-insensitive NAD(P)H dehydrogenase isolate d from yeast mitochondria. Here we show that platanetin inhibits exter nal NAD(P)H oxidation by intact potato (Solanum tuberosum L. cv. Bintj e) tuber mitochondria, deamino-NADH oxidation by Complex I assayed usi ng inside-out submitochondrial particles from these mitochondria, and rotenone-insensitive NAD(P)H oxidation by these submitochondrial parti cles. IACA was found to inhibit the oxidation of external NADH and suc cinate by intact mitochondria with similar efficiency. However, IACA a lso inhibited NADPH and duroquinol oxidation by intact mitochondria as well as deamino-NADH and NAD(P)H oxidation by inside-out submitochond rial particles. This indicates that IACA has several sites of inhibiti on in the electron transport chain. The lack of specificity of both pl atanetin and IACA prevents these inhibitors from being used to shed mo re light on the identity of the NAD(P)H dehydrogenases in plant mitoch ondria.