Hemocyanins are copper-containing oxygen carriers occurring freely dissolved in the hemolymph of many mollusks and arthropods. Hexamer of a number of different chains, of which A, B, and C have been identified. Hemolymph. The A chain contains two copper-binding sites (Ref.6, PubMed:2585484). Three histidine residues are ligands to each copper ion (Ref.6, PubMed:2585484). Belongs to the tyrosinase family. Hemocyanin subfamily.