Linked Life Data

3733708

Source:http://linkedlifedata.com/resource/pubmed/id/3733708

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
22
pubmed:dateCreated
1986-9-17
pubmed:abstractText
Nanosecond recombination time courses were measured by photolyzing O2, NO, CO, methyl, ethyl, n-propyl, n-butyl, and tert-butyl isocyanide complexes of sperm whale myoglobin with a 30-ns laser pulse at pH 7, 20 degrees C. Absorbance was measured both during and after the excitation pulse and as a function of laser light intensity. The results were analyzed quantitatively in terms of a three-step reaction scheme, MbX in equilibrium B in equilibrium C in equilibrium Mb + X, where Mb is myoglobin, B represents a geminate state in which the ligand is present in the distal pocket but not covalently bound to the iron atom, and C, a state in which the ligand is still embedded in the protein but further away from the heme group. The fitted rate parameters were required to be consistent with the observed overall quantum yield, Q, which had been measured independently using much longer (approximately 0.5 ms) xenon flash pulses. Three major conclusions were derived from these analyses. First, the overall quantum yield of the ligand complex is determined primarily by the competition between the rate of iron-ligand bond formation from the initial photoproduct, kB----MbX, and the rate of migration away from state B, kB----C. For example, kB----C approximately equal to 30-100 microseconds-1 for all three gaseous ligands, whereas both Q and kB----MbX vary over 3 orders of magnitude (i.e. NO, Q = 0.001, kB----MbX approximately equal to 16,000 microseconds-1; O2, Q = 0.1, kB----MbX approximately equal to 500 microseconds-1; CO, Q = 1.0, kB----MbX approximately equal to 2 microseconds-1). Second, for NO, O2, and the isonitriles, the rate-limiting step in the overall association reaction starting from ligand in solution is the formation of state B. The rate constant for this process varies from 2 X 10(7) M-1 s-1 for the gaseous ligands to 0.02-1.4 X 10(5) M-1 s-1 for the isonitriles. In contrast, the B to MbX transition is limiting for CO binding. Third, for all the ligands except CO, the overall rate of dissociation is limited significantly both by the rate of thermal bond disruption, kMbX----B, and the competition between geminate recombination and migration away from the distal pocket (i.e. kB----C/(kB----MbX + kB----C]. In the case of CO, the rate of bond disruption is equal to the observed dissociation rate constant.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Aug
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
5
pubmed:volume
261
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
10228-39
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1986
pubmed:articleTitle
A kinetic description of ligand binding to sperm whale myoglobin.
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