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S J Gill

Publications and source records attributed to S J Gill.

At least 37 records · Page 2Linked to original sources
PubMed1989

Allosteric formulation of thermal transitions in macromolecules, including effects of ligand binding and oligomerization.

We examine the effects of concentration (aggregation), buffers, and ligation, under conditions of either constant ligand activity or limited total amount of ligand, upon thermal denaturation of macromolecules as measured by scanning calorimetry. In doing so we utilize and extend an earlier generalized allosteric treatment [S. J. Gill, B. Richey, G. Bishop, and J. Wyman (1985) Biophys. Chem. 21, 1-14], applicable to ligand binding, enthalpy changes, and volume changes in a macromolecular system. The approach is contrasted with formulations based on the idea of structural domains. We show how information from the full scanning calorimetric curves can be utilized in arriving at and testing appropriate models for observed behavior in selected examples.

Allosteric Regulation↗
PubMed1988

Quantitative analysis of linkage in macromolecules when one ligand is present in limited total quantity.

We present a general framework for analysis of two closely related problems in biochemical studies: (1) The first is analysis of binding data obtained under conditions in which a second, linked ligand is present in limited total quantity. In such conditions the free activity of the second ligand varies throughout the primary ligand binding curve, and the resultant behavior can be quite complex. Analysis of such curves enables one to quantitatively extract detailed information regarding the linkage of the two ligands at intermediate stages of ligation. The treatment is applied in an accompanying paper to oxygen binding in human hemoglobin in the presence of organic phosphates [Robert, C.H., Fall, L., & Gill, S. J. (1988) Biochemistry (following paper in this issue)]. (2) The second treatment we outline regards the analogous problem of analyzing differential scanning calorimetry (DSC) data obtained for a macromolecule binding a ligand present in limited quantity. A simple model is presented that accounts for dual transitions like those already seen in DSC data for human serum albumin in the presence of nonsaturating amounts of fatty acids [Ross, P., & Shrake, A. (1987) Abstracts of the 42nd Calorimetry Conference, University of Colorado, Boulder, CO].

Binding Sites↗
PubMed1988

Linkage of organic phosphates to oxygen binding in human hemoglobin at high concentrations.

We have performed high-precision oxygen binding studies on human hemoglobin tetramers in the presence of a series of limited, subsaturating amounts of the effector compounds 2,3-diphosphoglycerate (DPG) and inositol hexaphosphate (IHP). The use of thin-layer optical methods enabled the use of high hemoglobin concentrations, preventing complications arising from the dissociation of the tetramer into dimers. Model-independent, simultaneous analysis of all data for each effector demonstrated that the intrinsic oxygen binding characteristics of the molecule are in agreement with those determined in earlier high-precision studies [e.g., Gill, S. J., Di Cera, E., Doyle, M. L., Bishop, G. A., & Robert, C. H. (1987) Biochemistry 26, 3995-4002] and that the affinity of the tetramer for the tightly binding effector IHP changes most markedly between the second and fourth oxygen binding steps, perhaps indicating a large conformational change. The data were then analyzed by using the truncated allosteric model [Di Cera, E., Robert, C. H., & Gill, S. J. (1987) Biochemistry 26, 4003-4008], which is based on the hypothesis that a quaternary conformational change occurs in the hemoglobin tetramer before the third and fourth oxygen molecules bind.

2,3-Diphosphoglycerate↗
PubMed1988

Nested allosteric interaction in tarantula hemocyanin revealed through the binding of oxygen and carbon monoxide.

We have examined the competitive binding of oxygen and carbon monoxide to the multisubunit hemocyanin of the tarantula Eurypelma californicum. Employment of high-precision thin-layer methods has enabled detailed characterization of the pure oxygen and pure carbon monoxide binding curves, as well as binding curves performed under mixed-gas conditions. The pure oxygen binding curve and the displacement of oxygen by carbon monoxide at full ligand saturation are highly cooperative, but in the absence of oxygen, carbon monoxide binds noncooperatively. The results were analyzed globally within the framework of a nested allosteric model [Robert, C.H., Decker, H., Richey, B., Gill, S.J., & Wyman, J. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1891-1895] which takes into account the hierarchy of subunit structure present in the macromolecule. The use of two ligands enables one to recognize two distinct levels of allosteric interaction functioning in the protein assembly. The binding characteristics of the allosteric states demonstrated for Eurypelma follow a similar pattern as those found earlier for Homarus americanus.

Allosteric Site↗
PubMed1988

Inhibition of bacterial ice nucleators by fish antifreeze glycoproteins.

Certain bacteria promote the formation of ice in super-cooled water by means of ice nucleators which contain a unique protein associated with the cell membrane. Ice nucleators in general are believed to act by mimicking the structure of an ice crystal surface, thus imposing an ice-like arrangement on the water molecules in contact with the nucleating surface and lowering the energy necessary for the initiation of ice formation. Quantitative investigation of the bacterial ice-nucleating process has recently been made possible by the discovery of certain bacteria that shed stable membrane vesicles with ice nucleating activity. The opposite effect, inhibition of ice formation, has been described for a group of glycoproteins found in different fish and insect species. This group of substances, termed antifreeze glycoproteins (AFGPs), promotes the supercooling of water with no appreciable effect on the equilibrium freezing point or melting temperature. Substantial evidence now indicates that AFGPs act by binding to a growing ice crystal and slowing crystal growth. As the ice-nucleating protein surface is believed to have a structure similar to an embryonic ice crystal, AFGPs might be predicted to interact directly with a bacterial ice-nucleating site. We report here that AFGPs from the antarctic fish Dissostichus mawsoni inhibit the ice-nucleating activity of membrane vesicles from the bacterium Erwinia herbicola. The inhibition effect shows saturation at high concentration of AFGP and conforms to a simple binding reaction between the AFGP and the nucleation centre.

Animals↗
PubMed1988

Alkaline Bohr effect of human hemoglobin Ao.

Differential oxygen binding measurements obtained over the pH range 6.95 to 9.10 at 25 degrees C have allowed a detailed description of the alkaline Bohr effect of human hemoglobin Ao. Phenomenological analysis of the data in terms of the Adair equation shows that: (1) the oxygen binding curves are asymmetrical with the population of the triply oxygenated species being negligible throughout the pH range studied: (2) the shape of the oxygen binding curve is affected by pH, especially at low saturation; and (3) the maximum O2-proton linkage is -0.52 mole of proton per mole of oxygen at pH 7.4. A possible molecular mechanism of the Bohr effect is proposed within the framework of an allosteric model which accounts for the low population of triply oxygenated hemoglobin species. At least three Bohr groups are necessary for a quantitative description of the alkaline Bohr effect. Two of these groups titrate in the range of the His146 beta and Vall alpha residues, which have long been identified as the main alkaline Bohr groups, and altogether contribute 84% of the alkaline Bohr effect at physiological pH. A third ionizable group, linked to oxygenation presumably at the beta chains, is implicated and is titrated in a pH range characteristic of a surface histidyl residue.

Allosteric Regulation↗
PubMed1988

Effect of differences in optical properties of intermediate oxygenated species of hemoglobin A0 on Adair constant determination.

Careful evaluation of the so-called isosbestic properties of oxygenated and deoxygenated hemoglobin spectra demonstrates that the spectral changes are not strictly linear with respect to the degree of saturation. In order to quantify the extent of nonlinearity, optical measurements of O2 binding to human hemoglobin were made at different wavelengths in the Soret region approaching the presumed isosbestic point. The results indicate that the extinction coefficient of intermediate oxygenated hemoglobin is 1% less than that of the fully oxygenated hemoglobin, with a resulting 3% (+/- 0.15%) nonlinearity effect on measurements taken at the peak of the oxygenated hemoglobin spectrum (414 nm). The lack of isosbestic conditions allows one to investigate the functional properties of the oxygenated intermediates directly. The small difference in the absorbance of different oxygenated species has practically no influence on the determination of Adair constants at wavelengths removed from the critical isosbestic region.

Hemoglobin A↗
PubMed1988

Analysis and parameter resolution in highly cooperative systems.

We have examined common methods of analysis of highly cooperative systems such as oxygen binding by hemoglobin and thermal denaturation. Through extensive simulation of ligand-binding data for a tetrameric macromolecule we show that careful attention must be paid to the formulation of the fitting function and to proper assessment of the number of parameters involved. We conclude that the partition function should be formulated in terms of overall reaction parameters as opposed to stepwise reaction parameters and that bias is introduced by fixing physical parameters such as extrapolated end points.

Ligands↗
PubMed1988

On the determination of species fractions from ligand-binding data. Application to human hemoglobin.

A method outlined in a previous study (S.J. Gill, H.T. Gaud, J. Wyman and G. Barisas, Biophys. Chem. 8 (1978) 53) is applied for the determination of species fractions from ligand-binding data for the oxygen reaction with human hemoglobin. The results obtained by this alternative approach, which is based on the solution of a system of linear equations, are consistent with those obtained using nonlinear least-squares analysis.

Hemoglobins↗
PubMed1988

A new method for the determination of equilibrium constants through binding capacity measurements.

The recent discovery of the negligible contribution of the triply ligated species to the oxygenation process of human hemoglobin A0 (S.J. Gill, E. Di Cera, M.L. Doyle, G.A. Bishop and C.H. Robert, Biochemistry 26 (1987) 3995) has pointed out the high precision of differential binding measurements. These measurements closely approximate the binding capacity (E. Di Cera, S.J. Gill and J. Wyman, Proc. Natl. Acad. Sci. U.S.A. 85 (1988) 449) of the system and can be used to calculate higher derivatives of the binding curve. We develop here a new method for the determination of equilibrium constants through binding capacity measurements by which the physical parameters expressing the optical properties of the system are eliminated in the data analysis.

Animals↗
PubMed1988

Canonical formulation of linkage thermodynamics.

The canonical structure of the group of thermodynamic potentials obtained from the energy of a physico-chemical system removes any possible distinction between physical and chemical binding phenomena. Transformations of these potentials by means of Jacobians give linkage relations for equilibrium thermodynamics. Linkage matrices are introduced to explore the functional properties of a biological macromolecule. They provide a quantitative basis for a broader approach and understanding of generalized binding phenomena.

Carbon Monoxide↗
PubMed1988

Binding capacity: cooperativity and buffering in biopolymers.

The group of linkage potentials resulting from the energy of a physicochemical system expressed per mol of a reference component, say a polyfunctional macromolecule, leads to the concept of binding capacity. This concept applies equally to both chemical and physical ligands and opens the way to consideration of higher-order linkage relationships. It provides a means of exploring the consequences of thermodynamic stability on generalized binding phenomena in biopolymers.

Biopolymers↗
PubMed1987

Thermodynamics of carbon monoxide binding to monomeric cytochrome c'.

The thermodynamic parameters for carbon binding to monomeric Rhodopseudomonas palustris cytochrome c' are determined. An enthalpy change for CO(aq) binding to the cytochrome is measured directly by titration calorimetry as -6.7 +/- 0.2 kcal/mol of heme, the CO binding equilibrium constant is measured at 35 degrees C as (1.96 +/- 0.05) X 10(5) M-1, and the binding equilibrium constant at 25 degrees C is calculated from the van't Hoff equation as (2.8 +/- 0.1) X 10(5) M-1. Comparison of the results to the known energetics of CO binding to dimeric cytochrome c', where the CO binding site is buried in the protein interior, indicates that the heme binding site on the monomer form is, in contrast, more exposed.

Carbon Monoxide↗
PubMed1987

Carbon monoxide binding to human hemoglobin A0.

The carbon monoxide binding curve to human hemoglobin A0 has been measured to high precision in experimental conditions of 600 microM heme, 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid, 0.1 M NaCl, 10 mM inositol hexaphosphate, 1 mM disodium ethylenediaminetetraacetic acid, pH 6.94, and 25 degrees C. Comparison to the oxygen binding curve in the same experimental conditions demonstrates that the two curves are not parallel. This result invalidates Haldane's two laws for the partitioning between carbon monoxide and oxygen to human hemoglobin. The partition coefficient is found to be 263 +/- 27 at high saturation, in agreement with previous studies, but is lowered substantially at low saturation. Although the oxygen and carbon monoxide binding curves are not parallel, both show the population of the triply ligated species to be negligible. The molecular mechanism underlying carbon monoxide binding to hemoglobin is consistent with the allosteric model [Di Cera, E., Robert, C. H., & Gill, S. J. (1987) Biochemistry 26, 4003-4008], which accounts for the negligible contribution of the triply ligated species in the oxygen binding reaction to hemoglobin [Gill, S. J., Di Cera, E., Doyle, M. L., Bishop, G. A., & Robert, C. H. (1987) Biochemistry 26, 3995-4002]. The nature of the different binding properties of carbon monoxide stems largely from the lower partition coefficient of the T state (123 +/- 34), relative to the R state (241 +/- 19).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Monoxide↗
PubMed1987

Carbon dioxide and oxygen linkage in human hemoglobin tetramers.

Differential binding curve measurements for oxygen in the presence of fixed carbon dioxide activities have allowed a detailed determination of the linkage between carbon dioxide and the oxygenated intermediates of human hemoglobin. Model-independent analysis of the data shows that at pH 7.4: (1) the oxygen binding curves are asymmetrical, the population of the triply oxygenated species being negligible; (2) the shape of the oxygen binding curve is invariant with carbon dioxide activity; (3) the maximum linkage is -0.32 moles carbon dioxide per mole oxygen; and (4) the overall carbon dioxide-dependent shift in the oxygen binding curve cannot be explained in terms of carbamino formation alone, the additional influence of bicarbonate being required. An allosteric model that accounts for the low population of triply oxygenated hemoglobin species is employed here as a framework from which to explore the carbon dioxide linkage mechanism at the intermediate stages of oxygenation. Carbon dioxide binding constants are found to be 780 M-1 and 580 M-1 for carbon dioxide binding to the deoxygenated alpha and beta chains, respectively, and 150 M-1 for carbon dioxide binding to the oxygenated form of both chains, as determined by simultaneous fitting of the oxygen binding curves with the model. Finally, by use of the determined binding polynomial for the carbon dioxide-oxygen linkage scheme, we have constructed a series of linkage graphs.

Allosteric Regulation↗
PubMed1987

Calorimetric studies of oxygen and carbon monoxide binding to human hemoglobin. Sequential binding heats for oxygen.

Two high precision techniques, titration microcalorimetry and thin-layer optical binding measurements, have made possible the evaluation of enthalpy changes for the overall oxygenation reactions for human hemoglobin (HbAo). Although the heat of adding three oxygen molecules could not be evaluated due to the indeterminate contribution of this species to the oxygen binding curve of the protein (Gill, S. J., Di Cera, E., Doyle, M. L., Bishop, G. A., and Robert, C. H. (1987) Biochemistry, 26, 3995-4002), the heats for binding two and four oxygen molecules were found to be simple multiples of the first binding heat. A direct consequence of equal stepwise heats is invariance of the shape of the binding curve with temperature, as pointed out by Wyman (Wyman, J. (1939) J. Biol. Chem. 127, 581-599). Titration microcalorimetry was also performed for the binding of carbon monoxide to hemoglobin. While the tight binding of CO precludes high-precision binding measurements, it does allow one to accurately determine the heat of ligation as a function of the CO bound. In these titrations a uniform heat of reaction is not observed, but the heat of binding increases markedly near the end point. This implies that the stepwise binding enthalpy for adding the third CO molecule is anomalously endothermic and for adding the fourth strongly exothermic. A similar phenomenon cannot be ruled out in the case of oxygen because of imprecision intrinsic in the analysis of the weaker ligand binding.

Calorimetry↗