ID 1.6.5.5 DE NADPH:quinone reductase. AN Quinone oxidoreductase. AN Zeta-crystallin. CA NADPH + 2 quinone = NADP(+) + 2 semiquinone. CF Zn(2+). CC -!- Specific for NADPH. CC -!- Catalyzes the one-electron reduction of certain quinones, with the CC orthoquinones 1,2-naphthoquinone and 9,10-phenanthrenequinone being CC the best substrates. CC -!- Dicoumarol (cf. EC 1.6.5.2) and nitrofurantoin are competitive CC inhibitors with respect to the quinone substrate. CC -!- The semiquinone free-radical product may be non-enzymically reduced CC to the hydroquinone or oxidized back to quinone in the presence of CC O(2). CC -!- Abundant in the lens of the eye of some mammalian species. PR PROSITE; PDOC00058; DR P28304, QOR1_ECOLI ; Q53FA7, QORX_HUMAN ; P11415, QOR_CAVPO ; DR Q08257, QOR_HUMAN ; Q28452, QOR_LAMGU ; P42865, QOR_LEIAM ; DR P47199, QOR_MOUSE ; Q0MVN8, QOR_PIG ; Q5R4S7, QOR_PONAB ; DR P43903, QOR_PSEAE ; Q6AYT0, QOR_RAT ; P40783, QOR_SALTY ; DR O74489, QOR_SCHPO ; P38230, QOR_YEAST ; Q9AYU1, QR1_TRIVS ; //