Linked Life Data

9354627

Source:http://linkedlifedata.com/resource/pubmed/id/9354627

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
44
pubmed:dateCreated
1997-12-4
pubmed:abstractText
Within the methylamine dehydrogenase (MADH)-amicyanin protein complex, long range intermolecular electron transfer (ET) occurs between tryptophan tryptophylquinone (TTQ) of MADH and the type I copper of amicyanin. The reoxidations of two chemically distinct reduced forms of TTQ were studied, a quinol (O-quinol) generated by reduction by dithionite and the physiologically relevant aminoquinol (N-quinol) generated by reduction by methylamine. The latter contains a substrate-derived amino group which displaces the C6 carbonyl oxygen on TTQ. ET from N-quinol MADH to amicyanin is gated by the transfer of a solvent exchangeable proton [Bishop, G. R., & Davidson, V. L. (1995) Biochemistry 34, 12082-12086]. The factors which influence this proton transfer (PT) reaction have been examined. The rate of PT increases with increasing pH and with increasing salt concentration. The salt effect is due to specific monovalent cations and is not a general ionic strength effect. The rate enhancements by pH and cations do not reflect an elimination of the PT step that gates ET. Over the range of pH from 5.5 to 9.0 and with cation concentrations from 0 to 200 mM, the observed rate of the redox reaction is still that of PT. This is proven by kinetic solvent isotope effect studies which show that a primary isotope effect persists even at the highest values of pH and cation concentration. A model is presented to explain how specific cations contribute to catalysis and influence the rate of PT in this reaction. The pH dependence is attributed to an ionizable group that is involved in cation binding. The effect of the cation is stabilization of a negatively charged reaction intermediate that is formed during the deprotonation of the N-quinol, and from which rapid ET to the copper of amicyanin occurs. The relevance of these findings to other enzymes which exhibit reaction rates that are influenced by monovalent cations is also discussed.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
4
pubmed:volume
36
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
13586-92
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1997
pubmed:articleTitle
Catalytic role of monovalent cations in the mechanism of proton transfer which gates an interprotein electron transfer reaction.
pubmed:affiliation
Department of Biochemistry, The University of Mississippi Medical Center, Jackson 39216-4505, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.