Inhibition of nitrogenase by NO
Liang, J.H.; Burris, R.H.
Indian Journal of Biochemistry and Biophysics 25(6): 636-641
1988
ISSN/ISBN: 0301-1208 PMID: 3255678 Document Number: 306055
The actions of a variety of inhibitors of nitrogenase have been studied in some detail, but the action of NO, an unusually strong inhibitor, has been neglected because it partially inactivates nitrogenase irreversibly. We have found with crude nitrogenase preparations from Clostridium pasteurianum that NO is a competitive inhibitor of both N2 and C2H2 reduction. NO also inhibits noncompetitively the reduction of C2H2 by purified nitrogenase from Azotobacter vinelandii. The nitrogenase exhibits two Km's for C2H2 reduction. Exposure for 15 min to a pNO as low as 1.25 pascals irreversibly inactivates purified nitrogenase reductase by 86%, whereas 20 pascals NO for 15 min gives no inactivation of dinitrogenase purified from A. vinelandii. NO also inhibits production of H2 by nitrogenase, although inhibition requires higher levels of NO than those needed to inhibit N2 reduction. The time courses of NO inhibition of N2 reduction and H2 production have been defined with a membrane leak mass spectrometer.