The reduction of flavodoxin from Azotobacter vinelandii by pyruvate.

The flavoprotein from Azotobacter, first isolated by SHETHNA et al. 1, is chemically well characterized, but its enzymatic function is still obscure. ARNON and coworkers 2 found this flavoprotein to be active in substituting for ferredoxin in the reduction of acetylene by a cell-free nitrogenase preparation from Azotobacter. We have recently confirmed their observation3. In addition, we could demonstrate that this flavoprotein is able to replace ferredoxin in the NADP+-reduction by either illuminated spinach chloroplasts or by molecular hydrogen and hydrogenase from Clostridium with a maximal efficiency of about 40 50% 3. Evidence was presented 3 that in catalysis the flavoprotein from Azotobacter functions as a substitute for a one electron carrier which shuttles between the fully reduced and the semiquinone form as do the flavodoxins 4?5. The experiments previously reported3 led to the conclusion that the flavoprotein from Azotobacter is — in its enzymatic functions — closely related to the class of flavodoxins, and, therefore, we suggested that the proper name to be used for this flavoprotein is flavodoxin from Azotobacter.