Ascorbate oxidase belongs, with L-ascorbate-cases and ceruloplasmin, to the group of enzymes usually referred to as the "blue" copper oxidases. These enzymes show very similar spectral properties related to copper atoms, which are at least four per enzyme molecule. Ascorbate oxidase is found mainly in plants. Copper atoms are present in blue oxidases in at least three different coordination environments and are classified as type-1, type-2, and type-3 copper according to the R. Malkin and B.J Malmstrom proposal. No animal copper enzymes having ascorbate oxidase activity have been isolated so far. Ascorbate oxidase is highly specific for compounds, like ascorbate, which contain a lactone ring with a vicinal enediol adjacent to a carbonyl group. Ascorbate oxidase became the subject of many biological and chemical investigations, especially by J.H. Dawson and associates. The purification of ascorbate oxidase from yellow crook-neck squash and green zucchini squash has been studied in great detail by Dawson and co-workers.