Purification and properties of two iron-sulfur proteins from Azotobacter vinelandii

Abstract

The purification to homogeneity, by the criteria of disc electrophoresis and ultracentrifugation, of two nonheme iron (iron-sulfur) proteins from Azotobacter vinelandii is described. The proteins have molecular weights of 21 000 ± 1 000 (I) and 24 000 ± 1 000 (II), respectively and contain two atoms of iron and labile sulfur per mole of protein. On reduction with dithionite, uptake of only one electron per molecule, i.e. per two iron atoms, leads to maximal decrease of light absorption and maximal development of the electron paramagnetic resonance (EPR) signal at g = 1.94, characteristic of the reduced forms. Iron and labile sulfur can be removed and apoproteins obtained, from which proteins can be reconstituted by the addition of iron and sulfide. These are identical, in all properties known, to the native proteins. Light absorption, circular dichroism and EPR spectra and other properties of the proteins are reported. The biological function of either protein is unknown.