<p>Haemocyanins are copper-containing oxygen transport proteins found in the haemolymph of many invertebrates. They are divided into 2 main groups, arthropodan and molluscan. These have structurally similar oxygen-binding centres, which are similar to the oxygen-binding centre of tyrosinases, however their quaternary structures are arranged differently. Copper active sites play a major role in biological dioxygen activation. Oxygen intermediates have been studied in detail for the proteins and enzymes involved in reversible O(2) binding (hemocyanin), activation (tyrosinase), and four-electron reduction to water (multicopper oxidases). Tyrosinase binds two copper ions (CuA and CuB). Each of the two copper ions has been shown to be bound by three conserved histidines residues. The arthropodan proteins exist as hexamers comprising 3 heterogeneous subunits and possess 1 oxygen-binding centre per subunit. Whereas, the molluscan proteins exist as cylindrical oligomers of 10 to 20 subunits and possess 7 or 8 oxygen-binding centres per subunit [<cite idref="PUB00000297"/>]. Although the proteins have similar amino acid compositions, the only real similarity in their primary sequences is in the region corresponding to the second copper-binding domain, which also shows similarity to the copper-binding domain of tyrosinases.</p> <p>Larval storage proteins (LSP) [<cite idref="PUB00002522"/>] are proteins from the hemolymph of insects, which may serve as a store of amino acids for synthesis of adult proteins. There are two classes of LSP's, arylphorins, which are rich in aromatic amino acids, and methionine-rich LSP's. LSP's form hexameric complexes that are structurally related to arthropods hemocyanins.</p> Hemocyanin-related larval storage protein arylphorin-related