Linked Life Data

17848549

Source:http://linkedlifedata.com/resource/pubmed/id/17848549

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
44
pubmed:dateCreated
2007-10-29
pubmed:abstractText
The latter stages of the catalytic cycle of the light-driven enzyme, protochlorophyllide oxidoreductase, have been investigated using novel laser photoexcitation methods. The formation of the ternary product complex was initiated with a 6-ns laser pulse, which allowed the product release steps to be kinetically accessed for the first time. Subsequent absorbance changes associated with the release of the NADP+ and chlorophyllide products from the enzyme could be followed on a millisecond timescale. This has facilitated a detailed kinetic and thermodynamic characterization for the interconversion of all the various bound and unbound product species. Initially, NADP+ is released from the enzyme in a biphasic process with rate constants of 1210 and 237 s(-1). The rates of both phases show a significant dependence on the viscosity of the solvent and become considerably slower at higher glycerol concentrations. The fast phase of this process exhibits no dependence on NADP+ concentration, suggesting that conformational changes are required prior to NADP+ release. Following NADP+ release, the NADPH rebinds to the enzyme with a maximum rate constant of approximately 72 s(-1). At elevated temperatures (>298 K) chlorophyllide is released from the enzyme to yield the free product with a maximum rate constant of 20 s(-1). The temperature dependencies of the rates of each of these steps were measured, and enthalpies and entropies of activation were calculated using the Eyring equation. A comprehensive kinetic and thermodynamic scheme for these final stages of the reaction mechanism is presented.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
2
pubmed:volume
282
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
32015-20
pubmed:meshHeading
pubmed:year
2007
pubmed:articleTitle
Laser excitation studies of the product release steps in the catalytic cycle of the light-driven enzyme, protochlorophyllide oxidoreductase.
pubmed:affiliation
Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom. derren.heyes@manchester.ac.uk
pubmed:publicationType
Journal Article