In molecular biology, multicopper oxidases are enzymes which oxidise their substrate by accepting electrons at a mononuclear copper centre and transferring them to a trinuclear copper centre; dioxygen binds to the trinuclear centre and, following the transfer of four electrons, is reduced to two molecules of water.

Structurally, these domains consist of a cupredoxin-like fold, a beta-sandwich consisting of 7 strands in 2 beta-sheets, arranged in a Greek-key beta-barrel.

[4] The family of multicopper oxidases can be divided into three groups based on the electron-donating substrate.

Multicopper oxidases include: In addition to the above enzymes there are a number of other proteins that are similar to the multi-copper oxidases in terms of structure and sequence, some of which have lost the ability to bind copper.

These include: copper resistance protein A (copA) from a plasmid in Pseudomonas syringae; domain A of (non-copper binding) blood coagulation factors V (Fa V) and VIII (Fa VIII);[8] yeast Fet3p (FET3) required for ferrous iron uptake;[9] yeast hypothetical protein YFL041w; and the fission yeast homologue SpAC1F7.08.