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

There is strong evidence that the iron-molybdenum cofactor (FeMoco) of nitr ogenase forms part of the enzyme's active site. FeMoco, a MoFe7S9. homocitr ate cluster, can be extracted intact from the enzyme into N-methylformamide solution but is reported to be inactive in substrate reduction unless powe rful reductants are used and then only acetylene and cyclopropene reduction s have been observed. The literature on the catalytic and substrate binding reactivities of extracted FeMoco is reviewed and new data on electrocataly tic hydrogen evolution presented. A comparison of the ligand binding proper ties of FeMoco from the wild-type and a NifV(-) mutant enzyme, which has ci trate in place of R-homocitrate, is presented. These data, are interpreted, in terms of their significance for enzyme turnover and of the obligate req uirement for R-homocitrate for dinitrogen reduction. (C) 1999 Elsevier Scie nce S.A. All rights reserved.