Purification and characterization of a flavohemoglobin from the denitrifying fungus <i>Fusarium oxysporum</i>

Abstract

A flavohemoprotein was purified to homogeneity from the denitrifying fungus Fusarium oxysporum. The purified protein existed as a monomer with a molecular weight of 44 kDa. It was purified in an oxidized form and exhibited the absorption maxima at 401, 540 and 643 nm in its resting form, and at 434 and 555 nm upon reduction with dithionite, respectively. The protein contained 0.5 mol protoheme/mol and 1.1 mol FAD/mol, respectively. When the resting flavohemoprotein was aerobically incubated with NAD(P)H, it was converted to a spectral species that is spectrally very similar to oxyhemoglobins. These properties are characteristics of flavohemoglobins (FHb) of Alcaligenes eutrophus, Escherichia coli, and baker's yeast. Further the amino terminal amino acid sequence of the protein of F. oxysporum was similar to those of these FHbs. These results suggest that the isolated flavohemoprotein of F. oxysporum would be a counterpart of the proteins in the FHb family.