PROPERTIES OF AZOFERREDOXIN PURIFIED FROM NITROGEN-FIXING EXTRACTS OF CLOSTRIDIUM PASTEURIANUM

Azoferredoxin has been purified 34-35 fold from N2-fixing extracts of Clostridium pasteurianum by three steps of protamine sulfate fractionation and Sephadex G-100 gel filtration. The protein contains two nonheme iron atoms and two acid-labile sulfide groups per molecular weight of 40 000. It is decolorized by the sodium salt of O-((3-hydroxymercuri-2-methoxypropyl)carbamyl)phenoxyacetic acid (mersalyl) and the effect of mersalyl on its spectrum is similar to the effect of mersalyl on the spectrum of ferredoxin. Azoferredoxin is cold labile and the rate of cold inactivation is decreased in the presence of 10% ethanol or 10% acetone. Exposure of azoferredoxin to O2 for 5 min causes complete inactivation. The effect of cold inactivation on azoferredoxin is different from that of oxidation as shown by distinct differences in spectral changes, measurable Fe2+ content and mercury titratable sulfhydryl and sulfide groups of the protein. © 1969.