In Vitro Formation of Assimilatory Reduced Nicotinamide Adenine Dinucleotide Phosphate: Nitrate Reductase from a Neurospora Mutant and a Component of Molybdenum-Enzymes

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Abstract
An active Neurospora -like assimilatory NADPH-nitrate reductase (EC 1.6.6.2), which can be formed in vitro by incubation of extracts of nitrate-induced Neurospora crassa mutant nit-1 with extracts of ( a ) certain other nonallelic nitrate reductase mutants, ( b ) uninduced wild type, or ( c ) xanthine oxidizing and liver aldehyde-oxidase systems was also formed by combination of the nit-1 extract with other acid-treated enzymes known to contain molybdenum. These molybdenum enzymes included ( a ) nitrogenase, or its molybdenum-iron protein, from Clostridium, Azotobacter , and soybeannodule bacteroids, ( b ) bovine liver sulfite oxidase, ( c ) respiratory formate-nitrate reductase from Escherichia coli , ( d ) NADH-nitrate reductase from foxtail grass ( Setaria faberii ), and ( e ) FADH 2 - and reduced methyl viologennitrate reductase preparations from certain Neurospora mutants. Several molybdenum-amino-acid complexes, as possible catalytic models of nitrogenase, were inactive (as were some previously tested 20 nonmolybdenum enzymes) in place of the acid-treated molybdenum-containing enzymes. The results imply the existence of a molybdenum-containing component shared by the known molybdenum-enzymes.