Linked Life Data

9107318

Source:http://linkedlifedata.com/resource/pubmed/id/9107318

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
1
pubmed:dateCreated
1997-5-1
pubmed:abstractText
The cytochrome (cyt) b subunit of ubihydroquinone: cytochrome c oxidoreductase (bc1 complex) contains four invariant glycine (G) residues proposed to be essential for proper packing of the high and low potential (bH and bL) hemes of the bc1 complex. One of these residues, G146 located in the transmembrane helix C of cyt b of Rhodobacter capsulatus, was substituted with A and V using site-directed mutagenesis, and the effects of these substitutions on the properties of the ubiquinone oxidation (Qo) site and heme bL of the bc1 complex were analyzed. The mutants G146A and V produced properly assembled but catalytically defective bc1 complexes that are unable to support photosynthetic growth. The steady-state ubihydroquinone: cytochrome c reductase activities of the mutant complexes were about one-tenth of that of a parental strain overproducing the wild-type enzyme. Similarly, their light-activated single turnover rates were significantly lower than those of a wild-type complex. The dark potentiometric titrations revealed no significant changes in the redox midpoint potentials (Em.7) of the high (bH) and low (bL) potential hemes of cyt b in both G146A and V mutants. However, EPR spectroscopy of the [2Fe-2S] cluster of the bc1 complex indicated that the Qo site of the mutant enzymes were unoccupied. Moreover, the gz signal of heme bL, but not that of heme bH, was modified both in G146A and V, suggesting that the geometry of its ligands has been distorted. These findings indicate that this region of cyt b must be well packed around heme bL since even a slight increase in the size of the amino acid side chain at position 146 (such as G to A) greatly perturbs the spatial conformation of heme bL, alters substrate accessibility and binding to the Qo site, and renders the bc1 complex inactive.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Mar
pubmed:issn
0006-3002
pubmed:author
pubmed:issnType
Print
pubmed:day
28
pubmed:volume
1319
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
99-108
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1997
pubmed:articleTitle
Substitutions at position 146 of cytochrome b affect drastically the properties of heme bL and the Qo site of Rhodobacter capsulatus cytochrome bc1 complex.
pubmed:affiliation
Department of Biology, University of Pennsylvania, Philadelphia 19104, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.