DI-IRON-CARBOXYLATE PROTEINS

Di-iron centers bridged by carboxylate residues and oxide/hydroxide gr oups have so far been seen in four classes of proteins involved in dio xygen chemistry or phosphoryl transfer reactions. The dinuclear iron c enters in these proteins are coordinated by histidines and additional carboxylate ligands. Recent structural data on some of these enzymes, combined With spectroscopic and kinetic data, can now serve as a base for detailed mechanistic suggestions. The di-iron sites in the major c lass of hydroxylase-oxidase enzymes, which contains ribonucleotide red uctase and methane monooxygenase, show significant flexibility in the geometry of their coordination of three or more carboxylate groups. Th is flexibility, combined with a relatively low coordination number, an d a buried environment suitable for reactive oxygen chemistry, explain s their efficient harnessing of the oxidation power of molecular oxyge n.