The rate-limiting step in O2 reduction by cytochrome ba3 from Thermus thermophilus

► Cytochrome ba3 (ba3) of T. thermophilus is a member of the heme-copper oxidase family. ► ba3 has a binuclear catalytic center comprised of a heme (heme a3) and a copper (CuB). ► The kinetics of the reaction of the enzyme with oxygen has a fast and a slow phase. ► The slow phase of the reaction is attributed to transient binding of oxygen to CuB.