Linked Life Data

7756294

Source:http://linkedlifedata.com/resource/pubmed/id/7756294

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
20
pubmed:dateCreated
1995-6-26
pubmed:abstractText
NADH peroxidase is a flavoenzyme having a single redox-active thiol, Cys42, that cycles between sulfenate and thiol forms in the NADH-dependent reduction of hydrogen peroxide. NADH peroxidase catalyzes the NADH-dependent reduction of quinones with turnover numbers between 1.2 and 3.9 s-1, per mole of FAD, at pH 7.5. The bimolecular rate constants for quinone reduction, V/K, ranged from 4.3 x 10(3) to 6.0 x 10(5) M-1 s-1 for 14 quinones whose redox potentials varied between -0.41 and 0.09 V. The logarithms of the V/K values for these quinones are hyperbolically dependent on their single-electron reduction potentials (E7(1). One-electron reduction of benzoquinone accounts for about 50% of the total electron transfer catalyzed by NADH peroxidase at pH 7, with the remainder of the reduction being catalyzed by a two-electron (hydride) transfer. Cys42 can be irreversibly oxidized to the sulfonate by hydrogen peroxide, with inactivation of the peroxidatic activity of the enzyme. The residual quinone reductase activity of NADH peroxidase which has undergone oxidative inactivation of the active site Cys42 indicates that this residue is not involved in the reduction of the quinones. Product inhibition studies suggest the possibility of overlap of the pyridine nucleotide and quinone binding sites in the reduced enzyme at low pH values. The pH dependence of the maximum velocity of naphthoquinone reduction shows that deprotonation of an enzymic group, exhibiting a pK value of ca. 6.2, decreases the maximal velocity. Primary deuterium kinetic isotope effects on V and V/K for quinone-dependent NADH oxidation increase upon protonation of a group, exhibiting a pK value of 6.4.(ABSTRACT TRUNCATED AT 250 WORDS)
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
23
pubmed:volume
34
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
6621-7
pubmed:dateRevised
2007-11-15
pubmed:meshHeading
pubmed:year
1995
pubmed:articleTitle
Quinone reductase reaction catalyzed by Streptococcus faecalis NADH peroxidase.
pubmed:affiliation
Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't