Xanthine Oxidase

I.U.B.: 1.1.3.22
Xanthine: O oxidoreductase

Enzymatic Reaction (image will open in a new window) 

Xanthine oxidase catalyzes the oxidation of xanthine to uric acid:

Characteristics of Xanthine Oxidase from Milk:

Xanthine oxidase, being a unimolecular, multicomponent electron transport systm, has been the target of extensive study employing electron paramagnetic resonance spectroscopy (Bray et al. 1964; Ehrenberg and Bray 1965; Handler et al. 1964; Nakamura and Yamazaki 1969). The enzyme has been reported to have anti-tumor effect in mice (Haddow et al. 1958) and to participate in the release of iron from hepatic ferritin stores in the plasma (Mazur et al. 1958).

Molecular weight:

275,000 (Hart et al. 1970).

Composition:

Each protein molecule contains 2 moles FAD, 2 gram-atoms Mo, and 8 gram-atoms Fe. The amino acid composition has been determined (Hart et al. 1970).

Extinction coefficient:

= 11.26 (Massey et al. 1969).

Optimum pH:

4.6 (Westerfeld et al. 1959).

Inhibitors:

Metal ions, urea, purine 6-aldehyde, 2-amino-4-hydroxypteridine 6-aldehyde (Westerfeld et al. 1959).

Stabilizers:

Salicylate, cysteine, histamine, and versenate act as stabilizers.

Specificity:

The enzyme has a broad specificity catalyzing the reduction of O₂, cytochrome c, NO^-3, Fe(CN)₆^-3 and various quinones and dyes by aldehydes and purines (Nakamura and Yamazaki 1969).

Stability:

Ammonium sulfate suspensions of the enzyme are stable for weeks when refrigerated, and for several days at room temperature.