title: Molecular characterization of human xanthine oxidoreductase: the enzyme is grossly deficient in molybdenum and substantially deficient in iron-sulphur centres.
abstract: XOR (xanthine oxidoreductase) purified from human milk was shown to contain 0.04 atom of Mo and 0.09 molecule of molybdopterin/subunit. On the basis of UV/visible and CD spectra, the human enzyme was approx. 30% deficient in iron-sulphur centres. Mo(V) EPR showed the presence of a weak rapid signal corresponding to the enzyme of low xanthine oxidase activity and a slow signal indicating a significant content of desulpho-form. Resulphuration experiments, together with calculations based on enzymic activity and Mo content, led to an estimate of 50-60% desulpho-form. Fe/S EPR showed, in addition to the well-known Fe/S I and Fe/S II species, the presence of a third Fe/S signal, named Fe/S III, which appears to replace partially Fe/S I. Comparison is made with similarly prepared bovine milk XOR, which has approx. 15-fold higher enzymic activity and Mo content. Taken along with evidence of low Mo content in the milk of other mammals, these findings add further support to the idea that XOR protein plays a physiological role in milk (e.g. in secretion) equal in importance to its catalytic function as an enzyme.
authors.affiliation: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK.
authors.forename: Benjamin L J
authors.initials: BL
authors.lastname: Godber
authors.forename: Guenter
authors.initials: G
authors.lastname: Schwarz
authors.forename: Ralf R
authors.initials: RR
authors.lastname: Mendel
authors.forename: David J
authors.initials: DJ
authors.lastname: Lowe
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bray
authors.forename: Robert
authors.initials: R
authors.lastname: Eisenthal
authors.forename: Roger
authors.initials: R
authors.lastname: Harrison
mesh_terms: D000818:Animals; D002417:Cattle; D003067:Coenzymes; D005260:Female; D006801:Humans; D007501:Iron / Q000032:analysis*; D008667:Metalloproteins; D008892:Milk / Q000201:enzymology; D008982:Molybdenum / Q000032:analysis*; D000090006:Molybdenum Cofactors; D009942:Organometallic Compounds / Q000737:chemistry; D011621:Pteridines / Q000737:chemistry; D013057:Spectrum Analysis; D013455:Sulfur / Q000032:analysis*; D014968:Xanthine Dehydrogenase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003067:Coenzymes; D007501:Iron; D008667:Metalloproteins; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D009942:Organometallic Compounds; D011621:Pteridines; D013455:Sulfur; D014968:Xanthine Dehydrogenase; C022261:molybdopterin