Electron Transport to Assimilatory Nitrate Reductase in A zotobacter vinelandii

Assimilatory nitrate reductase was particle-bound in extracts from Azotobacter vinelandii. Nitrate reduction by particle fractions was dependent on NADPH and a particle-bound electron carrier. When the enzyme was solubilized from the particles by treatment with detergents, the particle-bound electron carrier could be substituted by ferredoxin or flavodoxin. Flavodoxin reduced at the expense of photoreduced deazaflavin was much more efficient than ferredoxin in transferring electrons to nitrate reductase. The addition of both ferredoxin and flavodoxin to the assays with photoreduced deazaflavin gave additive effects. With the solubilized enzyme, NADPH only poorly supported nitrate reduction even after the addition of electron carriers. The experiments indicate that A. vinelandii utilizes an electron transport chain between NADPH and nitrate reductase with some properties similar to those described for the generation of reductants to nitrogenase.