Blue copper oxidases dioxygen binding

Ascorbate oxidase is a tetramer each subunit has 552 amino acids and contains 4 copper ions, the type-I blue copper center and the adjacent trinuclear center (arranged as a type-n center and a type-in dinuclear center) separated by /S-sheets (Figure 20) °. Ascorbate is oxidized to dehydroascorbate by dioxygen however, it is not bound directly to the metal center to be oxidized, but is proposed to bind near the type-I Cu site which may facihtate electron transfer to oxygen, presumably in the tri-Cu cluster site. Since humans cannot synthesize ascorbic acid, conservation of this important compound is highly regulated. For example, the oxidized ascorbate can be transported into red blood... 

The several functions of ceruloplasmin cannot be explained at present. It seems reasonable that this diversity is related to the activity of the copper centres. The general pattern of oxidase activity is probably similar to that of the other blue oxidases, with a type 3 binuclear site serving to bind and reduce dioxygen, with electrons transferred from the type 1 site. The type 2 copper may represent a substrate-binding site. 

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