Purification and properties of paramagnetic protein from clostridium pasteurianum W5

Abstract

The purification to homogeneity of the non-heme iron protein, sometimes referred to as either “red protein’ or “paramagnetic protein’, from Clostridium pasteurianum W5 extracts is described and its physicochemical properties studied. This paramagnetic protein ( g  1.94) has a molecular weight of about 25 000 and contains two iron and two acid-labile sulfur atoms per mol of protein. Its midpoint potential at pH 7.5, as determined by electron paramagnetic resonance titration, is —300 mV. Optical circular dichroism and electron paramagnetic resonance spectra of the paramagnetic protein are similar to those of two iron-two acid-labile sulfur ferredoxins. The biochemical reduction of the purified protein was also studied.