Kinetic studies on Klebsiella pneumoniae nitrogenase

Purified cell-free extracts of Klebsiella pneumoniae reduce N(2), N(3) (-), CN(-), or C(2)H(2) in the absence of an ATP-generating system when substrate concentrations of ATP are used. The optimum Mg(++)/ATP ratio is 0.5. Michaelis constants for the reduction of substrates calculated from kinetic studies of K. pneumoniae nitrogenase were similar to those that have been reported for Azotobacter vinelandii and Clostridium pasteurianum. Hill plots of the kinetic data are consistent with the view that there is a single binding site for each of the substrates N(2), C(2)H(2), CN(-), N(3) (-), and ATP. Inhibition studies of K. pneumoniae nitrogenase indicate that ADP competitively inhibits C(2)H(2) reduction. Also, the reducible substrates, N(3) (-) and CN(-), inhibit C(2)H(2) reduction. The inhibition by azide is noncompetitive, that by cyanide is mixed.