The heme-copper oxidase superfamily shares a Zn2+-binding motif at the entrance to a proton pathway

► Zn2+ inhibits C-type heme-copper oxidases. ► Zn2+ binds to a His near the entrance to the K-pathway analogue for protons. ► The Zn2+ binding motif is the same as in A-type oxidases. ► The Zn2+ motif occurs in evolutionary unrelated proteins.