Linked Life Data

12911304

Source:http://linkedlifedata.com/resource/pubmed/id/12911304

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
32
pubmed:dateCreated
2003-8-12
pubmed:abstractText
The bacterial photosynthetic reaction center (RC) uses light energy to catalyze the reduction of a bound quinone molecule Q(B) to quinol Q(B)H(2). In RCs from Rhodobacter sphaeroides the protons involved in this process come from the cytoplasm and travel through pathways that involve His-H126 and His-H128 located near the proton entry point. In this study, we measured the pH dependence from 4.5 to 8.5 of the binding of the proton transfer inhibitor Cd(2+), which ligates to these surface His in the RC and inhibits proton-coupled electron transfer. At pH <6, the negative slope of the logarithm of the dissociation constant, K(D), versus pH approaches 2, indicating that, upon binding of Cd(2+), two protons are displaced; i.e., the binding is electrostatically compensated. At pH >7, K(D) becomes essentially independent of pH. A theoretical fit to the data over the entire pH range required two protons with pK(A) values of 6.8 and 6.3 (+/-0.5). To assess the contribution of His-H126 and His-H128 to the observed pH dependence, K(D) was measured in mutant RCs that lack the imidazole group of His-H126 or His-H128 (His --> Ala). In both mutant RCs, K(D) was approximately pH independent, showing that Cd(2+) does not displace protons upon binding in the mutant RCs, in contrast to the native RC in which His-H126 and His-H128 are the predominant contributors to the observed pH dependence of K(D). Thus, Cd(2+) inhibits RC function by binding to functionally important histidines.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Aug
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
19
pubmed:volume
42
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
9626-32
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
2003
pubmed:articleTitle
Mechanism of proton transfer inhibition by Cd(2+) binding to bacterial reaction centers: determination of the pK(A) of functionally important histidine residues.
pubmed:affiliation
Department of Physics 0319, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA.
pubmed:publicationType
Journal Article, Comparative Study, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't