The effect of quaternary structure on the kinetics of conformational changes and nanosecond geminate rebinding of carbon monoxide to hemoglobin

Journal Article · Fri Apr 01 04:00:00 EST 1988 · Proceedings of the National Academy of Sciences of the United States of America; (USA)

DOI:https://doi.org/10.1073/pnas.85.7.2151· OSTI ID:6832540

Murray, L P; Hofrichter, J; Henry, E R; Eaton, W A ^[1]; Ikeda-Saito, Masao; Kitagishi, Keiko; Yonetani, Takashi ^[2]

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1. National Institutes of Health, Bethesda, MD (USA)
2. Univ. of Pennsylvania School of Medicine, Philadelphia (USA)

To determine the effect of quaternary structure on the individual kinetic steps in the binding of carbon monoxide to the {alpha} subunit of hemoglobin, time-resolved absorption spectra were measured after photodissociation of carbon monoxide from a hemoglobin tetramer in which cobalt was substituted for iron in the {beta} subunits. Cobalt porphyrins do not bind carbon monoxide. Spectra were measured in the Soret region at room temperature after time delays that varied from a few nanoseconds to the completion of ligand rebinding at about 100 ms. The results show that the liganded molecule is in the R state, but can be almost completely switched into the T state by the allosteric effectors inositol hexaphosphate and bezafibrate. The geminate yield, which is the probability that the ligand rebinds to the heme from within the protein, is found to be 40% for the R state and <1% for the T state. According to the simplest kinetic model, these results indicate that carbon monoxide enters the protein in the R and T quaternary conformations at the same rate, and that the 60-fold decrease in the overall binding rate, of carbon monoxide to the {alpha} subunit in the T state compared to the R state is almost completely accounted for by the decreased probability of binding after the ligand has entered the protein. The results further suggest that the low probability for the T state results from a decreased binding rate to the heme and not from an increased rate of return of the ligand to the solvent.

• OSTI ID: 6832540
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America; (USA), Journal Name: Proceedings of the National Academy of Sciences of the United States of America; (USA) Vol. 85:7; ISSN PNASA; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

560300* -- Chemicals Metabolism &amp; Toxicology
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ABSORPTION SPECTROSCOPY
BIOCHEMICAL REACTION KINETICS
BIOCHEMISTRY
BIOLOGICAL EFFECTS
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
COBALT COMPOUNDS
CROSS-LINKING
DECOMPOSITION
GLOBINS
HEMOGLOBIN
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
IRON COMPOUNDS
KINETICS
LASERS
NEODYMIUM LASERS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PIGMENTS
POLYMERIZATION
PORPHYRINS
PROTEINS
REACTION KINETICS
RELAXATION
SOLID STATE LASERS
SPECTROSCOPY
STRUCTURAL MODELS
TRANSITION ELEMENT COMPOUNDS