PNNL

Abstract

Iron-Sulfur clusters are found in all forms of life, which constitute the active sites of a growing list of proteins in such essential life-sustaining processes as respiration, nitrogen fixation, and photosynthesis (Spiro 1982). The most prototypical and ubiquitous Fe-S cluster is the cubane-type [4Fe-4S] cluster, which, in addition to its catalytic and regulatory roles, appears to be nature’s favorite agent for electron transfer and storage, such as in ferrodoxins (Fds), high-potential iron proteins (HiPIPs), and the integral machineries of hydrogenases and nitrogenases (Bernnert et al. 1997; Einsle etal. 2002; Peters et al. 1998). In proteins, the cubane [4Fe-4S] unit is usually coordinated by the amino acid cysteine. The [4Fe-4S] core functions as electron transfer agent usually between the following oxidation states: [4Fe-4S]1+ ? [4Fe-4S]2+ ? [4Fe-4S]3+ . A fourth state, the all-ferrous species [4Fe-4S]0, was also detected in the iron protein of nitrogenase.