Evidence for a copper-coordinated histidine-tyrosine cross-link in the active site of cytochrome oxidase

Following hints from X-ray data (Ostermeier C et al., 1997, Pi-oc Natl Acad Sci USA 94:10547-10553; Yoshikawa S et al., 1998, Science 280:1723-1729), chemical evidence is presented from four distantly related cytochrome-e oxidases for the existence of a copper(B)-coordinated His240-Tyr244) cross-link at the O-2-activating Heme Fea(3)-Cu-B center in the catalytic subunit I of the enzyme. The early evolutionary invention of this unusual structure may have prevented demaging (OH)-O-.-radical release at e(-)-transfer to dioxygen and thus have enabled O-2 respiration.