Linked Life Data

8034647

Source:http://linkedlifedata.com/resource/pubmed/id/8034647

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
29
pubmed:dateCreated
1994-8-15
pubmed:abstractText
The reductive half-reaction of milk xanthine dehydrogenase (XDH) with NADH and with xanthine has been studied at pH 7.5, 25 degree C. NADH reduces XDH to the two-electron reduced form at a rate of 18 s-1, independent of NADH concentration over the range studied. Further reduction by NADH to the four-electron state is inhibited by excess NADH. Subsequent binding of NADH to the four-electron reduced form of the enzyme causes the redistribution of one electron from the flavin to the molybdenum center. The four-electron reduced species reached through reduction by NADH is the same as the species obtained upon reaction of NAD with fully reduced XDH. In contrast, xanthine rapidly reduces XDH to the four-electron level; further reduction is comparatively slow and is inhibited by excess xanthine. Studies using substoichiometric xanthine show that the reaction of XDH with 1 equivalent of xanthine involves rapid substrate binding and rapid reduction of the molybdenum center of the enzyme. Before the release of urate from the molybdenum active site, an electron is transferred at 15 s-1 from the reduced molybdenum center to one of the iron-sulfur centers of XDH. Urate is then released at a rate of 13 s-1, followed by a rapid electron redistribution within the protein. The reductive half-reaction of XDH with xanthine is rate-limiting in xanthine/NAD turnover, which appears to occur between the two- and four-electron reduced enzyme species. The reduction of XDH by substoichiometric amounts of the fluorescent substrate xanthopterin was also studied. This reaction, monitored by changes in both absorbance and fluorescence, was found to involve the formation of two molybdenum complexes (an Eox.S complex and an Ered.P complex) followed by the release of the product, leucopterin.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Jul
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
22
pubmed:volume
269
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
18904-14
pubmed:dateRevised
2007-11-15
pubmed:meshHeading
pubmed:year
1994
pubmed:articleTitle
Studies of the reductive half-reaction of milk xanthine dehydrogenase.
pubmed:affiliation
Department of Biological Chemistry, University of Michigan, Ann Arbor 48109-0606.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S.