Heme-mediated oxygen activation in biology: cytochrome c oxidase and nitric oxide synthase.

Major advances have been made in our understanding of cytochrome c oxidase owing to continued crystallographic work on important intermediates. This, together with a wealth of data derived from selective mutations and sophisticated spectroscopic probes, has provided significant new insights into oxidase dioxygen chemistry and proton pumping activities. Recent advances have also been made for nitric oxide synthase, owing to the crystal structure determination of the heme domain for two of three nitric oxide synthase isoforms.