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| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:issue |
27
|
| pubmed:dateCreated |
1990-10-18
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| pubmed:abstractText |
Three hemoglobins have been isolated from the symbiont-harboring gill of the bivalve mollusc Lucina pectinata. Oxyhemoglobin I (Hb I), which may be called sulfide-reactive hemoglobin, reacts with hydrogen sulfide to form ferric hemoglobin sulfide in a reaction that may proceed by nucleophilic displacement of bound superoxide anion by hydrosulfide anion. Hemoglobins II and II, called oxygen-reactive hemoglobins, remain oxygenated in the presence of hydrogen sulfide. Hemoglobin I is monomeric; Hb II and Hb III self-associate in a concentration-dependent manner and form a tetramer when mixed. Oxygen binding is not cooperative. Oxygen affinities are all nearly the same, P50 = 0.1 to 0.2 Torr, and are independent of pH. Combination of Hb I with oxygen is fast; k'on = (estimated) 100-200 x 10(6) M-1 s-1. Combination of Hb II and Hb III with oxygen is slow: k'on = 0.4 and 0.3 x 10(6) M-1 s-1, respectively. Dissociation of oxygen from Hb I is fast relative to myoglobin: koff = 61 s-1. Dissociation from Hb II and Hb III is slow: koff = 0.11 and 0.08 s-1, respectively. These large differences in rates of reaction together with differences in the reactions of carbon monoxide suggest differences in configuration of the distal heme pocket. The fast reactions of Hb I are comparable to those of hemoglobins that lack distal histidine residues. Slow dissociation of oxygen from Hb II and Hb III suggest that a distal residue may interact strongly with the bound ligand. We infer that Hb I may facilitate delivery of hydrogen sulfide to the chemoautotrophic bacterial symbiont and Hb II and Hb III may facilitate delivery of oxygen. The midpoint oxidation-reduction potential of the ferrous/ferric couple of Hb I, 103 +/- 8 mV, was independent of pH. Potentials of Hb II and Hb III were pH-dependent. At neutral pH all three hemoglobins have similar midpoint potentials. The rate constant for combination of ferric Hb I with hydrogen sulfide increases 3000-fold from pH 10.5 to 5.5, with apparent pK 7.0, suggesting that undissociated hydrogen sulfide is the attacking ligand. At the acid limit combination of ferric Hb I with hydrogen sulfide, k'on = 2.3 x 10(5) M-1 s-1, is 40-fold faster than combination with ferric Hb II or myoglobin.(ABSTRACT TRUNCATED AT 400 WORDS)
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| pubmed:grant | |
| pubmed:language |
eng
|
| pubmed:journal | |
| pubmed:citationSubset |
IM
|
| pubmed:chemical |
http://linkedlifedata.com/resource/pubmed/chemical/Amino Acids,
http://linkedlifedata.com/resource/pubmed/chemical/Carboxyhemoglobin,
http://linkedlifedata.com/resource/pubmed/chemical/Heme,
http://linkedlifedata.com/resource/pubmed/chemical/Hemoglobins,
http://linkedlifedata.com/resource/pubmed/chemical/Ligands,
http://linkedlifedata.com/resource/pubmed/chemical/Macromolecular Substances,
http://linkedlifedata.com/resource/pubmed/chemical/Oxyhemoglobins,
http://linkedlifedata.com/resource/pubmed/chemical/Sulfides
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| pubmed:status |
MEDLINE
|
| pubmed:month |
Sep
|
| pubmed:issn |
0021-9258
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| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:day |
25
|
| pubmed:volume |
265
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| pubmed:owner |
NLM
|
| pubmed:authorsComplete |
Y
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| pubmed:pagination |
16043-53
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| pubmed:dateRevised |
2007-11-14
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| pubmed:meshHeading |
pubmed-meshheading:2398044-Amino Acids,
pubmed-meshheading:2398044-Animals,
pubmed-meshheading:2398044-Bacteria,
pubmed-meshheading:2398044-Bivalvia,
pubmed-meshheading:2398044-Carboxyhemoglobin,
pubmed-meshheading:2398044-Chromatography, Gel,
pubmed-meshheading:2398044-Chromatography, Ion Exchange,
pubmed-meshheading:2398044-Electrophoresis, Polyacrylamide Gel,
pubmed-meshheading:2398044-Heme,
pubmed-meshheading:2398044-Hemoglobins,
pubmed-meshheading:2398044-Kinetics,
pubmed-meshheading:2398044-Ligands,
pubmed-meshheading:2398044-Macromolecular Substances,
pubmed-meshheading:2398044-Molecular Weight,
pubmed-meshheading:2398044-Oxidation-Reduction,
pubmed-meshheading:2398044-Oxyhemoglobins,
pubmed-meshheading:2398044-Protein Binding,
pubmed-meshheading:2398044-Spectrophotometry,
pubmed-meshheading:2398044-Sulfides,
pubmed-meshheading:2398044-Symbiosis
|
| pubmed:year |
1990
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| pubmed:articleTitle |
Hemoglobins of the Lucina pectinata/bacteria symbiosis. I. Molecular properties, kinetics and equilibria of reactions with ligands.
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| pubmed:affiliation |
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461.
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| pubmed:publicationType |
Journal Article,
Research Support, U.S. Gov't, P.H.S.,
Research Support, U.S. Gov't, Non-P.H.S.
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