Binds 1 copper ion per subunit. Binds 2 calcium ions per subunit. Contains 1 topaquinone per subunit. Binds 1 Mn(2+) ion per subunit. Homodimer. Prismatic layer of shell (at protein level). Expressed primarily in the mantle with highest level in the mantle edge and lower level in the mantle pallium. Topaquinone (TPQ) is generated by copper-dependent autoxidation of a specific tyrosyl residue. Belongs to the copper/topaquinone oxidase family.