The Genetic Control of Molybdoflavoproteins in Aspergillus nidulans. A Xanthine Dehydrogenase I Half-Molecule in cnx- Mutant Strains of Aspergillus nidulans

Abstract

The cnx- group of mutants of A. nidulans lacks xanthine dehydrogenase (xanthine: NAD+ oxidoreductase, EC 1.2.1.37) and nitrate reductase (EC 1.6.6.3) activities and are thought to be defective in the synthesis of a molybdenum-containing cofactor, cnx, common to xanthine dehydrogenase and nitrate reductase. The cnx cofactor has a role in maintaining the aggregated multimeric structure of nitrate reductase. In cnx- mutants grown under conditions inducing xanthine dehydrogenase I, a species cross-reacting with antisera to the native enzyme and of half its MW is present, together with cross-reacting molecules of similar MW to the native enzyme. This suggests that the cnx cofactor has a role in maintaining the aggregated structure of xanthine dehydrogenase I. Both cross-reacting species are capable of passing reducing equivalents from NADH to a tetrazolium salt, showing that the cnx cofactor is not necessary for enzymic activity towards NADH.