Quinone reductases of higher plants

NAD(P)H: quinone oxidoreductase (DT-diaphorase) was detected in 100000 x g supernatant fractions of extracts of a wide variety of higher plants. Smaller amounts were also found in microsomes and chloroplast fractions. The enzyme was partially purified from soluble extracts of several plants and the quinone reductase from Catharanthus roseus was enriched 25-fold. Plant quinone reductases have molecular weights in the range of 38000-53000 as determined by gel filtration. The plant enzyme is far less sensitive to dicoumarol than its mammalian counterpart and it is inhibited by superoxide dismutase. Quinone reductase is capable of reducing simple p-benzoquinone and naphthoquinone including vitamins K3 and K1. These results indicate that, although the plant enzyme exhibits a similar substrate specificity, it is distinguishable from mammalian DT-diaphorase particularly with respect to its mechanism of reduction.