Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Brian J. Hales

Abstract

The inhibitor CO was used to investigate the mechanism of Mo and V nitrogenase. While low pressures of CO enhanced, high pressures inhibited V nitrogenase-catalyzed C$\rm\sb2H\sb6$ formation. This is not the case for $\rm C\sb2H\sb4$ formation, where the rate of electron flux determined if CO acted as an enhancer or inhibitor. A two-site model is proposed, in which CO binding to one site enhances, and CO binding to both sites inhibits product formation. Replacement of CO(g) by Ar or $\rm C\sb2H\sb2$ resulted in correlated decay of hi-CO and development of lo-CO EPR signals, suggesting that the two signals arise from one metal cluster. The detection of CO binding to the lo-CO form of the enzyme in the absence of turnover suggests that CO stabilizes a MoFe protein cluster or turnover state and enhances binding of additional CO molecules. $\sp{13}$CO and $\sp{57}$Fe ENDOR studies of Mo nitrogenase in moderate flux demonstrated that (i) lo-CO Mo nitrogenase has one bound CO molecule and hi-CO enzyme has two; (ii) the second CO binds to the same cluster that has one bound CO; and (iii) CO binds to the FeMo cofactor and not to the P cluster.

ISBN

9780591288957

Pages

182

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