Some Properties of Two Forms of Nitrite Reductase from Corn (Zea mays L.) Scutellum

Nitrite reductase from corn scutellum—a non-chlorophyllous tissue—can use methyl viologen, benzyl viologen or ferredoxin as electron donor. Little or no reduction occurs with nicotinamide or flavin nucleotides. Activity is inhibited by p-chloromercuribenzoate and by cyanide. Organic chelates, with the exception of bathocuproine disulphonate and bathophenanthroline disulphonate, are not inhibitory. Ammonia is the reaction product. Ion exchange chromatography resolves the nitrite reductase activity into two peaks which apparently represent two forms of the enzyme. Both have a molecular weight of 61—63000 as determined by molecular exclusion chromatography, and a pH optimum of 6.7—6.8. Although their properties are generally similar, they show a marked difference in thermal stability, ionic charge and behaviour during isoelectric focusing. Nitrite reductase is found largely in the soluble fraction although some particulate activity is also obtained. Both forms of the enzyme are present in the soluble and particulate fractions.