Abstract
Here, we report the impact of substitution for the α-70Val residue of Azotobacter vinelandii nitrogenase molybdenum-iron (MoFe) protein on the so-called “hi-CO” CO bound complex as monitored in real-time by stopped-flow infra-red (SF-IR) spectroscopy. Nitrogenase is a bacterial metalloenzyme system whose physiological function is to catalyze the reduction of dinitrogen to ammonia [1, 2] with a concomitant reduction of 2H+ to H2 and hydrolysis of MgATP. X-ray crystallography on MoFe nitrogenase reveals the active-site FeMo-cofactor to be an unprecedented [Fe7S9MoX:homocitrate] cluster [3, 4], figure 1. However, simple inspection of this structure does not provide an obvious location for substrate binding or any indication of the subsequent mechanism for substrate reduction. Mechanisms focused on substrate binding to either Mo and Fe sites have been proposed as have combination approaches that involve migration of substrate-derived moieties between metal atoms during reduction [5–8].
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