Allosteric interpretation of haemoglobin properties

Shulman, R. G.; Hopfield, J. J.; Ogawa, Satoshi

doi:10.1017/s0033583500001840

Cited by 212 publications

(123 citation statements)

References 122 publications

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“…As a result, the IHP binding switched the quaternary state (because the molecules minimized their energy), yet the number of oxygens bound remained constant. The quaternary state, with and without IHP, was identi ed by using the NMR markers of quaternary structure in solution that had previously been established (18). Most of these resonances were distant from the heme and had been observed in either the fully ligated or fully unligated Hb molecules, yet some were heme resonances.…”

Section: Nmr and The Mwc Modelmentioning

confidence: 99%

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Spectroscopic Contributions to the Understanding of Hemoglobin Function: Implications for Structural Biology

Shulman¹

2001

IUBMB Life

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Section: Nmr and The Mwc Modelmentioning

confidence: 99%

“…The experiments showed that an intermediate degree of ligation such as T2 or R2 could facilitate the switch (16)(17)(18)(19). In the MWC quaternary-linked model, the ligand af nity should switch with state.…”

Section: Nmr and The Mwc Modelmentioning

confidence: 99%

Spectroscopic Contributions to the Understanding of Hemoglobin Function: Implications for Structural Biology

Shulman¹

2001

IUBMB Life

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“…The role of hemoglobin as the paradigm for understanding cooperative interactions in multisubunit proteins has been questioned in recent years because of confusion in the literature concerning the applicability of the two-state allosteric mechanism of Monod, Wyman, and Changeux (MWC), and the stereochemical mechanism of Perutz (P) (Monod et al, 1965;Perutz, 1970;Edelstein, 1973;Shulman et al, 1975;Pemtz et al, 1987). According to the twostate MWC model, cooperativity results from a shift in the population of molecules from the low-affinity ( T ) quaternary structure to the high-affinity (R) quaternary structure as successive oxygen molecules bind, and not from subunit interactions within a single quaternary structure.…”

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Allosteric effectors do not alter the oxygen affinity of hemoglobin crystals

et al. 1997

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Abstract:In solution, the oxygen affinity of hemoglobin in the T quaternary structure is decreased in the presence of allosteric effectors such as protons and organic phosphates. To explain these effects, as well as the absence of the Bohr effect and the lower oxygen affinity of T-state hemoglobin in the crystal compared to solution, Rivetti C et al. (1993a. Biochemistry 32:2888-2906 suggested that there are high-and low-affinity subunit conformations of T, associated with broken and unbroken intersubunit salt bridges. In this model, the crystal of T-state hemoglobin has the lowest possible oxygen affinity because the salt bridges remain intact upon oxygenation. Binding of allosteric effectors in the crystal should therefore not influence the oxygen affinity. To test this hypothesis, we used polarized absorption spectroscopy to measure oxygen binding curves of single crystals of hemoglobin in the T quaternary structure in the presence of the "strong" allosteric effectors, inositol hexaphosphate and bezafibrate. In solution, these effectors reduce the oxygen affinity of the T state by 10-30-fold. We find no change in affinity (

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“…Efficient oxygen transport by hemoglobin depends on alteration of its affinity in the course of ligand binding. A wide range of kinetic and equilibrium data is described successfully by a two-state, or allosteric model (1), which posits that the affinities are chiefly controlled by the quaternary structure of hemoglobin. The parameters of this model are the ligand binding and release rates for each of the two structures (R and T) and a set of rates for conversion between the R and T structures with zero to four ligands bound to the tetramer.…”

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Rate of quaternary structure change in hemoglobin measured by modulated excitation.

Ferrone¹,

Hopfield²

1976

Proc. Natl. Acad. Sci. U.S.A.

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Using a novel technique of modulated photodissociation of carbon monoxide from hemoglobin, we have obtained the rates for conversion between the two quaternary states, R and T, at 3fold ligation. Our measurements at pH 7 and 220 give rates of 780 + 40 sec1 for going from R to T, and 2500 i 200 secI from T to R. This yields an equilibrium constant of 0.31 + 0.04, which is in good agreement with previous estimates. The degree of agreement between this equilibrium constant and that predicted from the allosteric model provides a new, quantitative test of the allosteric description. A sequential model for the change in structure was found incompatible with the data, even if kinetic subunit inequivalence was assumed. The technique described here is quite general and can be used as long as the system under investigation can be repetitively excited in a regime in which it responds linearly to the excitation. Efficient oxygen transport by hemoglobin depends on alteration of its affinity in the course of ligand binding. A wide range of kinetic and equilibrium data is described successfully by a two-state, or allosteric model (1), which posits that the affinities are chiefly controlled by the quaternary structure of hemoglobin. The parameters of this model are the ligand binding and release rates for each of the two structures (R and T) and a set of rates for conversion between the R and T structures with zero to four ligands bound to the tetramer. The model requires that the binding and release rates be independent of the degree or level of ligation, although the interconversion rates may differ for the various degrees of ligation. Despite their importance to the model, there have been few measurements of any rates of change between conformational states (2-4), and no measurements of rate pairs from which equilibrium constants between the R and T structures might be obtained.We have studied the kinetics of the binding of the last ligand to the 3fold ligated tetramer by means of modulated excitation, and thereby measured the rates of conversion between R and T structures. This method of kinetic study has unique abilities in measuring the time constants of molecular processes that have similar spectral changes and similar time constants. The technique differs from conventional kinetics in that an excitation is repetitively applied and phase-sensitive detection is used. The latter is superior to signal averaging since it permits large signals to be nulled, revealing much weaker relaxation components. With this method, the optical absorption spectrum of the excited species can be obtained simply by scanning a monochromator, so that the separation of different components in the relaxation is assisted by the wealth of information available from static spectra. We have used a mechanically chopped light beam to drive our Hb(CO)4 sample out of equilibrium. A second beam-the analyzing beam-also passes through the sample to a photodetector. The signal from this detector is fed to a lock-in amplifier. The analyzing beam is mo...

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Allosteric interpretation of haemoglobin properties

Cited by 212 publications

References 122 publications

Spectroscopic Contributions to the Understanding of Hemoglobin Function: Implications for Structural Biology

Spectroscopic Contributions to the Understanding of Hemoglobin Function: Implications for Structural Biology

Allosteric effectors do not alter the oxygen affinity of hemoglobin crystals

Rate of quaternary structure change in hemoglobin measured by modulated excitation.

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