Abstract
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 Clostridium pasteurianum 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 mµ with a shoulder at 472 mµ, 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. pasteurianum with an effectiveness of 70, 40, and 30%, respectively. It is suggested that flavodoxin replaces ferredoxin as an electron carrier in cells of C. pasteurianum grown in an iron-deficient medium since these cells contain less than 5% of the ferredoxin found in cells grown in an iron-sufficient medium.
Highlights
PuriJication of Flavodoxin Crude Extract-Dried C. pasteurianum cells, 44 g grown on a medium low in iron, were mixed with 440 ml of Hz0 in a l-liter
As in the hydrogen evolution system, flavodoxin replaces ferredoxin as an electron carrier
The absorption spectrum of flavodoxin is similar to the spectra of well characterized flavoproteins
Summary
Acetyl phosphate formation was linear from 0 to 5 mpmoles of flavodoxin per 1.1 ml. The elastic system catalyzed the formation of less than 0.2 mpmole of acetyl phosphate in the absence of added ferredoxin or flavodoxin. As in the hydrogen evolution system, flavodoxin replaces ferredoxin as an electron carrier. At 3 mpmoles/ 1.1 ml, flavodoxin is 40% as effective as equimolar ferredoxin
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