Exploring the reactivity of the isolated iron-molybdenum cofactor of nitrogenase

Abstract

There is strong evidence that the iron-molybdenum cofactor (FeMoco) of nitrogenase forms part of the enzyme’s active site. FeMoco, a MoFe 7S 9·homocitrate cluster, can be extracted intact from the enzyme into N-methylformamide solution but is reported to be inactive in substrate reduction unless powerful reductants are used and then only acetylene and cyclopropene reductions have been observed. The literature on the catalytic and substrate binding reactivities of extracted FeMoco is reviewed and new data on electrocatalytic hydrogen evolution presented. A comparison of the ligand binding properties of FeMoco from the wild-type and a NifV − mutant enzyme, which has citrate in place of R-homocitrate, is presented. These data are interpreted in terms of their significance for enzyme turnover and of the obligate requirement for R-homocitrate for dinitrogen reduction.