Linked Life Data

10346906

Source:http://linkedlifedata.com/resource/pubmed/id/10346906

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
21
pubmed:dateCreated
1999-6-23
pubmed:abstractText
Electron transfer within complexes of cytochrome c (Cc) and cytochrome c peroxidase (CcP) was studied to determine whether the reactions are gated by fluctuations in configuration. Electron transfer in the physiological complex of yeast Cc (yCc) and CcP was studied using the Ru-39-Cc derivative, in which the H39C/C102T variant of yeast iso-1-cytochrome c is labeled at the single cysteine residue on the back surface with trisbipyridylruthenium(II). Laser excitation of the 1:1 Ru-39-Cc-CcP compound I complex at low ionic strength results in rapid electron transfer from RuII to heme c FeIII, followed by electron transfer from heme c FeII to the Trp-191 indolyl radical cation with a rate constant keta of 2 x 10(6) s-1 at 20 degrees C. keta is not changed by increasing the viscosity up to 40 cP with glycerol and is independent of temperature. These results suggest that this reaction is not gated by fluctuations in the configuration of the complex, but may represent the elementary electron transfer step. The value of keta is consistent with the efficient pathway for electron transfer in the crystalline yCc-CcP complex, which has a distance of 16 A between the edge of heme c and the Trp-191 indole [Pelletier, H., and Kraut, J. (1992) Science 258, 1748-1755]. Electron transfer in the complex of horse Cc (hCc) and CcP was examined using Ru-27-Cc, in which hCc is labeled with trisbipyridylruthenium(II) at Lys-27. Laser excitation of the Ru-27-Cc-CcP complex results in electron transfer from RuII to heme c FeII with a rate constant k1 of 2.3 x 10(7) s-1, followed by oxidation of the Trp-191 indole to a radical cation by RuIII with a rate constant k3 of 7 x 10(6) s-1. The cycle is completed by electron transfer from heme c FeII to the Trp-191 radical cation with a rate constant k4 of 6.1 x 10(4) s-1. The rate constant k4 decreases to 3.4 x 10(3) s-1 as the viscosity is increased to 84 cP, but the rate constants k1 and k3 remain the same. The results are consistent with a gating mechanism in which the Ru-27-Cc-CcP complex undergoes fluctuations between a major state A with the configuration of the hCc-CcP crystalline complex and a minor state B with the configuration of the yCc-CcP complex. The hCc-CcP complex, state A, has an inefficient pathway for electron transfer from heme c to the Trp-191 indolyl radical cation with a distance of 20.5 A and a predicted value of 5 x 10(2) s-1 for k4A. The observed rate constant k4 is thus gated by the rate constant ka for conversion of state A to state B, where the rate of electron transfer k4B is expected to be 2 x 10(6) s-1. The temperature dependence of k4 provides activation parameters that are consistent with the proposed gating mechanism. These studies provide evidence that configurational gating does not control electron transfer in the physiological yCc-CcP complex, but is required in the nonphysiological hCc-CcP complex.
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
25
pubmed:volume
38
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
6846-54
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed-meshheading:10346906-2,2'-Dipyridyl, pubmed-meshheading:10346906-Animals, pubmed-meshheading:10346906-Cations, pubmed-meshheading:10346906-Cysteine, pubmed-meshheading:10346906-Cytochrome c Group, pubmed-meshheading:10346906-Cytochrome-c Peroxidase, pubmed-meshheading:10346906-Electron Transport, pubmed-meshheading:10346906-Free Radicals, pubmed-meshheading:10346906-Horses, pubmed-meshheading:10346906-Ion Channel Gating, pubmed-meshheading:10346906-Macromolecular Substances, pubmed-meshheading:10346906-Models, Molecular, pubmed-meshheading:10346906-Mutagenesis, Site-Directed, pubmed-meshheading:10346906-Organometallic Compounds, pubmed-meshheading:10346906-Oxidation-Reduction, pubmed-meshheading:10346906-Photolysis, pubmed-meshheading:10346906-Ruthenium, pubmed-meshheading:10346906-Saccharomyces cerevisiae
pubmed:year
1999
pubmed:articleTitle
Role of configurational gating in intracomplex electron transfer from cytochrome c to the radical cation in cytochrome c peroxidase.
pubmed:affiliation
Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville 72701, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S.