Linked Life Data

8611587

Source:http://linkedlifedata.com/resource/pubmed/id/8611587

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
8
pubmed:dateCreated
1996-6-5
pubmed:abstractText
Neuronal NO synthase (nNOS) consists of a reductase domain that binds FAD, FMN, NADPH, and calmodulin, and an oxygenase domain that binds heme, tetrahydrobiopterin, and the substrate L-arginine. One flavin in resting nNOS exits as an air-stable semiquinone radical. During NO synthesis, electron transfer occurs between the flavins and heme iron. We have characterized the nNOS heme iron and flavin semiquinone radical by electron paramagnetic resonance (EPR) spectroscopy. Under anaerobic conditions, the flavin radical spin relaxation was very slow (8 HZ at 22 K) and was enhanced 13-fold by dissolved dioxygen via spin-spin coupling. The flavin radical, probably the semiquinone FMNH., was shown by progressive microwave power saturation and EPR saturation recovery under anaerobic conditions to be spin-spin coupled with the heme iron located in the nNOS oxygenase domain. Analysis of an nNOS preparation that was devoid of heme but contained the flavin radical revealed that spin-spin coupling increased the rate of flavin radical relaxation by a factor of 15. The presence of bound substrate (L-arginine) or the substate analogue Nomega-nitro-L-arginine methyl ester (NAME) had no effect on the flavin spin relaxation kinetics. The observed g values of the nNOS heme were 7.68, and 1.81 and were unchanged by occupation of the substrate binding site by L-arginine or NAME. The substrate also had no effect on the heme zero-field splitting parameter, D=5.2cm-1. Together, the data indicate that the flavin and heme redox centers are positioned near each other in nNOS, consistent with their participating in an interdomain electron transfer. The flavin radical is affected by dissolved oxygen, suggesting that its binding site within the reductase domain partially exposed to solvent, but is unaffected when substrate binds to the oxygenase domain. Substrate binding also appears to take place outside the first coordination shell of the nNOS heme iron.
pubmed:grant
pubmed:commentsCorrections
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
27
pubmed:volume
35
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
2804-10
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1996
pubmed:articleTitle
EPR spectroscopic characterization of neuronal NO synthase.
pubmed:affiliation
Department of Chemistry, Yale University, New Haven, Connecticut 06511, USA.
pubmed:publicationType
Journal Article, In Vitro, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't