Effect of high pN2 and high pD2 on ammonia production, hydrogen evolution, and hydrogen deuteride formation by nitrogenases

Abstract

The effect of the partial pressure of N2 (pN2) and deuterium (pD2) on HD formation, H2 evolution and NH3 production by nitrogenases from Klebsiella pneumoniae and Clostridium pasteurianum was studied. By using pressures up to 4 atm, the concentration ranges of N2 and D2 in these investigations were extended beyond those used in previous studies. The pN2 dependence of HD formation with constant pD2 ideally shows no HD formation under zero pN2, reaches a peak which depends on the pD2, and then decreases to zero at very high pN2. K. pneumoniae and C. pateurianum nitrogenases differ in their Ki(D2) for N2 fixation. C. pasteurianum nitrogenase had the lower activity for formation of HD. With K. pneumoniae nitrogenase, D2 enhanced H2 evolution from 31% of the electron flux partitioned to H2 in the absence of D2 to 51% of the electron flux partitioned to H2 at 400 kilopascals of D2. With C. pasteurianum nitrogenase, the equivalent values were 33% and 48% of the total electron flux. These results support the mechanism for nitrogenase-catalyzed reductions proposed by W.W. Cleland.