A Free Radical Flavoprotein from Azotobacter

Abstract

Abstract A flavoprotein containing flavin mononucleotide has been isolated from Azotobacter vinelandii, purified to homogeneity, and crystallized. Anaerobically prepared flavoprotein exhibited free radical properties and absorption maxima at 580 and 615 mµ, suggestive of a flavin semiquinone. The flavoprotein is unusual in that the oxidized form reacts slowly even with strong reducing agents (Na2S2O4) and is resistant to reduction beyond the half-reduced state; anaerobically prepared flavoprotein is exceptionally resistant to oxidation by molecular oxygen. These unusual properties have been shown to be dependent upon the structural integrity of the protein.