Kinetics of MgATP-dependent Iron Chelation from the Fe-protein of the Azotobacter vinelandiiNitrogenase Complex

Chelation of Fe from the Fe-protein component (Av2) of Azotobacter vinelandiinitrogenase has been investigated. The chelation, which requires MgATP binding by Av2, is best described as a two-exponential process. The rates for the two phases differed by ∼ 10-fold and increased as the concentration of MgATP was increased. The rates for both phases were 50% of maximum at approximately 1.5 mMMgATP. At MgATP concentrations greater than 100 µM, the more rapid phase represented ∼ 25% of the total Fe chelated from Av2. However, below 100 µMMgATP, the proportion of the faster phase decreased until at 20 µMMgATP, only a single phase could be detected.