The interface between the biological and inorganic worlds: iron-sulfur metalloclusters.

Complex iron-sulfur metalloclusters form the active sites of the enzymes that catalyze redox transformations of N2, CO, and H2, which are likely components of Earth's primordial atmosphere. Although these centers reflect the organizational principles of simpler iron-sulfur clusters, they exhibit extensive elaborations that confer specific ligand-binding and catalytic properties. These changes were probably achieved through evolutionary processes, including the fusion of small clusters, the addition of new metals, and the development of cluster assembly pathways, driven by selective pressures resulting from changes in the chemical composition of the biosphere.