Electron transfer properties of iron-sulfur proteins

The details of most electron transfer reactions involving iron-sulfur prote ins have remained undisclosed because of the lack of experimental methods s uitable to measure precisely the relevant rates. Nuclear magnetic resonance (NMR) provides a powerful means to overcome these problems, at least with selected proteins. A combination of NMR studies and site-directed mutagenes is experiments has been instrumental in defining both the site of interacti on and the main trends of the intracomplex electron transfer in the case of rubredoxin electron self-exchange. Analysis of the NMR data obtained for m ixtures of different redox levels of several 2[4Fe-4S] ferredoxins provided both first-order, for intramolecular, and second-order, for intermolecular , rate constants. Their dependence as a function of structural changes gave insight into the mechanism of electron transfer in this type of protein. C ontrary to some expectations, the high-spin [4Fe-4Se](+) clusters assembled in isopotential ferredoxins do not change the intramolecular electron tran sfer rate as compared to low-spin [4Fe-4s](+) homologs. In combination with activity measurements, the kinetic data have been used to model the electr on transfer competent complexes between Clostridium pasteurianum ferredoxin and the main enzymes acting as redox partners in vivo. (C) 2000 Elsevier S cience Inc. All rights reserved.