Molybdenum-free nitrate reductases from vanadate-reducing bacteria

Two catalytically distinct molybdenum-free dissimilatory nitrate reductases , a soluble periplasmic and a membrane-bound one, were isolated from the va nadate-reducing facultatively anaerobic bacterium Pseudomonas isachenkovii and purified to electrophoretic homogeneity, The enzymes did not contain mo lybdenum, the periplasmic enzyme contained vanadium, whereas the membrane-b ound enzyme was vanadium-free. Both nitrate reductases lacked molybdenum co factor. This fact was proved by reconstitution of the apoprotein of the nit rate reductase of Neurospora crassa nit-1 mutant. This is the first demonst ration of molybdenum-free and molybdenum cofactor-free nitrate reductases. (C) 1998 Federation of European Biochemical Societies.