Characterization of a soluble ferric reductase from Neisseria gonorrhoeae

An NADH-dependent ferric reductase was identified in extracts of Neisseria gonorrhoeae. Enzyme activity was measured in an assay using ferrozine as the ferrous iron acceptor. Ferric reductase activity was enhanced by Mg2+ and flavine nucleotides. The enzyme reduced both citrate- and diphosphate-bound ferric iron as well as ferric hydroxide (Imferon). However, no activity was observed with either 30%-iron-saturated transferrin or with the gonococcal iron-binding protein, Fbp. The ferric reductase was found primarily within the cytoplasmic cell fraction. The soluble ferric reductase was purified 110-fold by ammonium sulfate precipitation, gel and anion-exchange chromatography. Results obtained following gel chromatography and SDS/polyacrylamide gel electrophoresis suggested that the enzyme had a molecular mass of about 25 kDa.