PRESENCE OF HEME IN THE TUNGSTEN ANALOG OF NITRATE REDUCTASE AND ITS RELATIONSHIP TO DEHYDROGENASE FUNCTION

Spinach plants were grown for 8 weeks in sand culture with either complete nutrient containing molybdate (0.05 p.p.m.) or molybdenum-free nutrient containing tungstate (1 p.p.m.). Nitrate reductase and its tungsten analogue were extracted and purified. Nitrate reductase activities (units/kg leaf) decreased during purification from 22.72 to 4.59 (molybdate plants) and from 2.19 to 0.86 (tungstate plants). Cytochrome c reductase activities decreased from 211 to 26 (molybdate plants) and from 539 to 22 (tungstate plants) reflecting the super-induction of the small molecular size enzyme and decreased stability of the analogue. Both nitrate reductase and its analogue contained similar amounts of cytochrome b557kg leaf, which was reduced by NADH and reoxidised by excess of the dehydrogenase electron acceptor dichlorophenolindophenol. Only the haem in the enzyme from molybdate plants was reoxidisable by nitrate. © 1979.