Isolation and characteristics of flavodoxin from nitrogen-fixing Clostridium pasteurianum.

The purification, crystallization, and biological activity of flavodoxin is reported. It is a new electron transport protein and has been isolated from extracts of cells of Closfridium pasfeurianum grown on nitrogen gas or ammonia and in an iron-deficient medium. Flavodoxin forms yellow crystals from ammonium sulfate solution, has a molecular weight of 14,600, absorption maxima of the oxidized form at 272, 372, 443 rnp with a shoulder at 472 mp, and contains no iron, molybdenum, cobalt, or labile sulfur. In equimolar amounts, it will substitute for ferredoxin in the metabolism of hydrogen and pyruvate and in the fixation of nitrogen by extracts of C. pasfeurianum with an effectiveness of 70,40, and 30%, respectively. It is suggested that flavodoxin replaces ferredoxin as an electron carrier in cells of C. pasfeurianum grown in an iron-deficient medium since these cells contain less than 5% of the ferredoxin found in cells grown in an ironsufficient medium.