A Voltammetric Study of Nitrogenase Catalysis Using Electron Transfer Mediators

Document Type

Article

Journal/Book Title

ACS Catalysis

Publication Date

1-4-2019

Publisher

American Chemical Society

Volume

9

Issue

2

First Page

1366

Last Page

1372

Abstract

Nitrogenase catalyzes the reduction of an array of small molecules, including N 2 to NH 3 , by delivering electrons and protons to substrates bound to the active site metal cluster FeMo-cofactor. A challenge in describing the mechanism of nitrogenase-catalyzed reduction reactions is quantifying electron flow through the enzyme to different substrates. In this study, a mediated cyclic voltammetry approach was developed that provides a quantitative analysis of electron flow through nitrogenase. Conditions were optimized to reveal the catalytic reaction rate-limiting step. Analysis of the current response by an electrochemical approach yielded a catalytic rate constant (k cat ) of 14 s -1 , consistent with earlier studies. The current approach was used to resolve a long-standing conundrum in nitrogenase research, the apparent inhibition of electron flow through nitrogenase with increasing partial pressures of N 2 . It was demonstrated using this voltammetric approach in the absence of the reductant dithionite that total electron flow through nitrogenase remains constant up to a N 2 partial pressure of 1 atm.

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