Linked Life Data

11293550

Source:http://linkedlifedata.com/resource/pubmed/id/11293550

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
2001-4-9
pubmed:abstractText
The heme of neuronal nitric oxide synthase (nNOS) participates in O2 activation but also binds self-generated NO, resulting in reversible feedback inhibition. We utilized mutagenesis to investigate if a conserved tryptophan residue (Trp409), which engages in pi-stacking with the heme and hydrogen bonds to its axial cysteine ligand, helps control catalysis and regulation by NO. Mutants W409F and W409Y were hyperactive regarding NO synthesis without affecting cytochrome c reduction, reductase-independent N-hydroxyarginine oxidation, or Arg and tetrahydrobiopterin binding. In the absence of Arg electron flux through the heme was slower in the W409 mutants than in wild-type. However, less NO complex accumulated during NO synthesis by the mutants. To understand the mechanism, we compared the kinetics of heme-NO complex formation, rate of heme reduction, kcat prior to and after NO complex formation, NO binding affinity, NO complex stability, and its reaction with O2. During the initial phase of NO synthesis, heme-NO complex formation was three and five times slower in W409F and W409Y, which corresponded to a slower heme reduction. NO complex formation inhibited wild-type turnover 7-fold but reduced mutant turnover less than 2-fold, giving mutants higher steady-state activities. NO binding kinetics were similar among mutants and wild type, although mutants also formed a 417 nm ferrous-NO complex. Oxidation of ferrous-NO complex was seven times faster in mutants than in wild type. We conclude that mutant hyperactivity primarily derives from slower heme reduction and faster oxidation of the heme-NO complex by O2. In this way Trp409 mutations minimize NO feedback inhibition by limiting buildup of the ferrous-NO complex during the steady state. Conservation of W409 among NOS suggests that this proximal Trp may regulate NO feedback inhibition and is important for enzyme physiologic function.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0162-0134
pubmed:author
pubmed:issnType
Print
pubmed:volume
83
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
301-8
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2001
pubmed:articleTitle
A proximal tryptophan in NO synthase controls activity by a novel mechanism.
pubmed:affiliation
Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, OH 44195, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.