|Protein Name||Xanthine dehydrogenase/oxidase|
|Ref Sequence Id||NP_776397.1|
|Amino Acid Lenth||1332|
|Protein Existence Status||Reviewed: Experimental evidence at protein level|
|Presence in other biological fluids/tissue/cells||Blood, heart, liver, intestine, endothelial cells and at the luminal surface of rat liver sinusoidal endothelial cells,|
|Protein Function||catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid; source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various pathways; may induce mutagenesis, cell proliferation, and tumor progression, but they are also associated with apoptosis and cell differentiation; XOR activity generates free radicals and other oxidant reactive species resulting in either harmful or beneficial outcomes; modulate endothelial function and arteriolar tone; may be cytotoxic|
|Biochemical Properties||Represents more than 8% of the intrinsic protein in MFGM;homodimer; oxidizes in the presence of NAD+ or NADP+ as electron acceptors; bacterial XDHs usually show better catalytic activity and thermal stability than eukaryotic XDHs but both display optimum catalytic activity at nearly neutral pH and relatively low temperatures, and very limit pH-activity range; mammalian enzyme exists in two interconvertible forms, xanthine dehydrogenase and xanthine oxidase; can be interconverted reversibly by sulphide reagents or irreversibly by proteolysis; specificity is low for methylene blue and 2.6-dichlorophenolindophenol, ferricyanide, and many quinones; inactive forms are demolybdo or desulfo; XOR inhibitors are allopurinol, oxypurinol or analogues|
|Significance in milk||Antimicrobial activity; natural antibiotic; encourages breas-feeding in infants; generates hydrogen peroxide|
|PTMs||Bovine XOR is not glycosylated; human XO is N-glycosylated; goat MFGM XO contains sialic acids in O-linked glycosylation|
|PDB ID||1fiq, 1fo4, 1n5x, 1v97, 1vdv, 3am9, 3amz, 3ax7, 3ax9, 3b9j, 3bdj, 3etr, 3eub, 3nrz, 3ns1, 3nvv, 3nvw, 3nvy, 3nvz, 3sr6, 3una, 3unc, 3uni,|
|Additional Comments||XOR activity is upreglated in ischaemia that increases ROS; XOR production increases in brain meningitis;|
|Bibliography||1. Hancock, J. T., Salisbury, V., Ovejero-Boglione, M. C., Cherry, R., Hoare, C., Eisenthal, R., and Harrison, R. (2002) Antimicrobial properties of milk: dependence on presence of xanthine oxidase and nitrite. Antimicrob. Agents Chemother. 46, 3308–3310. |
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7. Gutteridge, S., Tanner, S. J., and Bray, R. C. (1978) Comparison of the molybdenum centres of native and desulpho xanthine oxidase. The nature of the cyanide-labile sulphur atom and the nature of the proton-accepting group. Biochem. J. 175, 887–897.
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10. Miyamoto, Y., Akaike, T., Yoshida, M., Goto, S., Horie, H., and Maeda, H. (1996) Potentiation of nitric oxide-mediated vasorelaxation by xanthine oxidase inhibitors. Proc. Soc. Exp. Biol. Med. 211, 366–373.
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