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I Denisov

Publications and source records attributed to I Denisov.

6 recordsLinked to original sources
PubMed2000

Confirmation of a unique intra-dimer cooperativity in the human hemoglobin alpha(1)beta(1)half-oxygenated intermediate supports the symmetry rule model of allosteric regulation.

The contribution of the alpha(1)beta(1)half-oxygenated tetramer [alphabeta:alphaO(2)betaO(2)] (species 21) to human hemoglobin cooperativity was evaluated using cryogenic isoelectric focusing. The cooperative free energy of binding, reflecting O(2)-driven protein structure changes, was measured as (21)DeltaG(c) = 5.1 +/- 0. 3 kcal for the Zn/FeO(2) analog. For the Fe/FeCN analog, (21)DeltaG(c) was estimated as 4.0 kcal after correction for a CN ligand rearrangement artifact, demonstrating that ligand rearrangement does not invalidate previous conclusions regarding this species. In the context of the entire Hb cooperativity cascade, which includes eight intermediate species, the 21 tetramer is highly abundant relative to the other doubly-ligated species, providing strong support for the previously determined consensus partition function of O(2) binding and for the Symmetry Rule model of hemoglobin cooperativity (Ackers et al., Science 1992;255:54-63). Cooperativity of normal human hemoglobin is shown to depend on site-configuration, and not solely the number of O(2) bound, nor the occupancy of alpha vs. beta subunits. Verification of a unique contribution from the alpha(1)beta(1)doubly-oxygenated species to the equilibrium O(2) binding curve strongly reinforces the Symmetry Rule interpretation that the alpha(1)beta(1)dimer acts both as a structural and functional element in cooperative O(2) binding.

Allosteric Regulation↗
PubMed1999

The kinetics of the reaction between NO and O2 as studied by a novel approach.

The kinetics of the reaction between NO and O2 was determined by measuring the time course of the decrease in the concentration of NO with a quench-flow technique. NO and O2 were mixed rapidly and reacted for periods of time varying from 10 to 50 s. A second rapid mixing with a solution containing an excess of deoxyhemoglobin and sodium hydrosulfite trapped free NO as nitrosylhemoglobin and reduced O2. The spectrum of the mixture of deoxy- and nitrosylhemoglobin was recorded within 30 s from the second mixing, before any appreciable dissociation of NO from the protein, by means of a flow-cell mounted on-line with the quench-flow apparatus. The amount of NO not consumed in the auto-oxidation reaction was calculated from the proportion of nitrosylhemoglobin in the mixture. As NO and O2 bind deoxyhemoglobin at comparable rates and NO is oxidized to nitrate by oxyhemoglobin, the ratio of hemoglobin/(NO + O2) had to be optimized to avoid the interference of this oxidation reaction. The kinetics was first and second order with respect to O2 and NO, respectively and third order overall with a rate constant k = 4 x kaq = 4 x 2.23 (+/- 0.26) x 10(6) M-2 s-1 at 20 degrees C, invariant in the pH range 7-9, in agreement with published values obtained by different methodologies.

Computer Simulation↗
PubMed1997

Thermodynamic stability of the asymmetric doubly-ligated hemoglobin tetramer (alpha+CNbeta+CN)(alphabeta): methodological and mechanistic issues.

Free energy contributions to cooperativity by the eight ligation intermediates of human hemoglobin (Hb) have been characterized extensively using six oxygenation analogs [cf. Huang et al. (1996) Biophys. J. 71, 2094-2105, Table 2]. These unprecedented data bses have strongly supported the molecular code mechanism of Hb cooperativity [Ackers et al. (1992) science 255, 54-83]. The present study addresses a recent argument against this work [Shibayama et al. (1997) Biochemistry 36, 4375-4381] based on "free energy" determinations for a doubly-ligated species of the CN-met analog. Shibayama et al. (1997) have claimed that, in the hybridization experiments that have been used to determine free energy of the asymmetric "species[21]" tetramer, a portion of the bound cyanide is allegedly released from CN-met Hb during the incubation with deoxy Hb that is used to achieve hybrid equilibrium. These authors have claimed that cyanide release has resulted in extensive electron exchange between heme sites of the hybridizing sample, leading to incorrect evaluation of the equilibrium species population by the cryogenic techniques that have been employed. In this report, we demonstrate that neither appreciable cyanide loss nor electron exchange occurs with the methods that have been used extensively by our two laboratories for these equilibrium determinations [Perrella et al. (1990) Biophys. Chem. 35, 97-103; Daugherty et al. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 1110-1114]. An alternative experiment, which Shibayama et al. (1997) have carried out to illustrate their claim, does not evaluate a thermodynamic equilibrium property of the species [21] hybrid. The relevance of their newly-estimated "free energy" is therefore unclear. Nevertheless, Shibayama et al. (1997) have claimed that their proposed "free energy" (which is approximately 1.3 kcal more positive than the free energy of -11.4 kcal found independently by our two laboratories) renders invalid the molecular code mechanism of hemoglobin cooperativity. This representation is utterly without foundation since a free energy even more positive than suggested by Shibayama et al. (1997) would be fully consistent with the molecular code mechanism.

Animals↗
PubMed1996

Functional heterogeneity of the alpha and beta subunits in the association reaction between hemoglobin and carbon monoxide.

A technique is described for the rapid inactivation and removal of excess ferricyanide used for the non-cryogenic oxidation of the unliganded subunits of the intermediates in the association reaction between hemoglobin and carbon monoxide. Under these conditions the asymmetric oxidized intermediates, which dissociate into non-identical dimers, disproportionate into their parent tetramers and four species, Hb+, HbCO, alpha 2+ beta 2CO, alpha 2CO beta 2+, are isolated by non-cryogenic isoelectric focusing. The relative concentrations of species alpha 2CO beta 2+ and alpha 2+ beta 2CO measure the overall distribution of the ligand between the alpha and beta subunits in the association reaction. At 20 degrees C in 0.1 M KCl, pH 7, preferential CO binding to the beta subunits was observed, in agreement with observations made by the cryogenic technique for the isolation of the intermediates [M. Perrella, N. Davids and L. Rossi-Bernardi, J. Biol. Chem. 267 (1992) 8744].

Carbon Monoxide↗