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

Abstract
Following hints from X‐ray data (Ostermeier C et al., 1997, Proc 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‐c oxidases for the existence of a copperB‐coordinated His240–Tyr244) cross‐link at the O2‐activating Heme Fea3–CuB center in the catalytic subunit I of the enzyme. The early evolutionary invention of this unusual structure may have prevented demaging OH‐radical release at e‐transfer to dioxygen and thus have enabled O2 respiration.