Linked Life Data

9931033

Source:http://linkedlifedata.com/resource/pubmed/id/9931033

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
1999-2-23
pubmed:abstractText
Conserved and semiconserved acidic and basic residues of the beta subunit of the proton-pumping nicotinamide nucleotide transhydrogenase from Escherichia coli potentially involved in proton pumping were investigated. Out of 16 charged residues studied, 6 have not been previously investigated. The most dramatic effects of mutation were observed with beta H91, beta D392, and beta K424. beta H91E showed a pronounced shift of the pH optimum for both reduction of thio-NADP+ by NADH (forward reaction) and reduction of 3-acetylpyridine-NAD+ by NADPH (reverse reaction) to lower pH. This mutant catalyzed a cyclic reduction of 3-acetylpyridine-NAD+ by NADH in the presence of NADP(H) with a pH profile also shifted toward a lower pH. These results are consistent with a mechanism where the normal forward and reverse reactions are indeed limited by protonation/deprotonation of beta H91. The cyclic reaction was affected by mutations of beta H91, probably through conformational changes involving the active NADP(H) site. The beta D392A mutant was inactive with regard to forward and reverse reactions, but showed a wild-type-like pH dependence for the partly active cyclic reaction. However, Km,app for NADP(H) in this reaction was elevated 50-100-fold, suggesting that beta D392 is located in or near the NADP(H)-binding site. Transhydrogenases contain a conserved beta K424-beta R425-beta S426 sequence that has been proposed to be important for NADP(H) binding. beta K424R was strongly inhibited and showed an 18-fold increased Km,app for NADPH in the reverse reaction as compared to wild type. Consequently, this mutation affected all NADP(H)-linked activities and essentially abolished the unspecific interaction of NAD(H) with this site. The pH dependences of the forward and reverse reactions, as well as the cyclic reaction, were shifted to a lower pH as compared to the wild-type enzyme, and the salt dependence was also altered.
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
2
pubmed:volume
38
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
1652-8
pubmed:dateRevised
2011-11-17
pubmed:meshHeading
pubmed:year
1999
pubmed:articleTitle
Site-directed mutagenesis of charged and potentially proton-carrying residues in the beta subunit of the proton-translocating nicotinamide nucleotide transhydrogenase from Escherichia coli. Characterization of the beta H91, beta D392, and beta K424 mutants.
pubmed:affiliation
Department of Biochemistry and Biophysics, Göteborg University, Chalmers University of Technology, Sweden.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't