The terminal oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. Subunits 1-3 form the functional core of the enzyme complex. Subunit 2 transfers the electrons from caldariella quinol to the bimetallic center of the catalytic subunit 1 that is formed by heme A3 and Cu(B). 2 a quinol + O2 = 2 a quinone + 2 H2O Belongs to the cytochrome c oxidase subunit 2 family.