Linked Life Data

11853453

Source:http://linkedlifedata.com/resource/pubmed/id/11853453

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
8
pubmed:dateCreated
2002-2-20
pubmed:abstractText
A cross-linked histidine-phenol compound was synthesized as a chemical analogue of the active site of cytochrome c oxidase. The structure of the cross-linked compound (compound 1) was verified by IR, (1)H and (13)C NMR, mass spectrometry, and single-crystal X-ray analysis. Spectrophotometric titrations indicated that the pK(a) of the phenolic proton on compound 1 (8.34) was lower than the pK(a) of tyrosine (10.1) or of p-cresol (10.2). This decrease in pK(a) is consistent with the hypothesis that a cross-linked histidine-tyrosine may facilitate proton delivery to the binuclear site in cytochrome c oxidase. Time-resolved optical absorption spectra of compound 1 at room temperature, generated by excitation at 266 nm in the presence and absence of dioxygen, indicated a species with absorption maxima at approximately 330 and approximately 500 nm, which we assign to the phenoxyl radical of compound 1. The electron paramagnetic resonance (EPR) spectra of compound 1, obtained after UV photolysis, confirmed the generation of a paramagnetic species at low temperature. Because the cross-linked compound lacks beta-methylene protons, the EPR line shape was dramatically altered when compared to that of the tyrosyl radical. However, simulation of the EPR line shape and measurement of the isotropic g value was consistent with a small coupling to the imidazole nitrogen and with little spin density perturbation in the phenoxyl ring. The ground-state Fourier transform infrared (FT-IR) spectrum of compound 1 showed that addition of the imidazole ring perturbs the frequency of the tyrosine ring stretching vibrations. The difference FT-IR spectrum, associated with the oxidation of the cross-linked compound, detected significant perturbations of the phenoxyl radical vibrational bands. We postulate that phenol oxidation produces a small delocalization of spin density onto the imidazole nitrogen of compound 1, which may explain its unique optical spectral properties.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0002-7863
pubmed:author
pubmed:issnType
Print
pubmed:day
27
pubmed:volume
124
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1750-60
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2002
pubmed:articleTitle
Modeling the active site of cytochrome oxidase: synthesis and characterization of a cross-linked histidine-phenol.
pubmed:affiliation
Department of Chemistry and Biochemistry, University of California Santa Cruz, California 95064, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't