Allosteric equilibria in the binding of fibrinogen to platelets.

The binding of fibrinogen to platelets occurs according to the law of mass action. The platelet receptor binds reversibly a single fibrinogen molecule and undergoes a conformational transition between two allosteric states, T and R, that differ in their affinity for fibrinogen. The equilibrium between the two forms is shifted by ADP toward the R (high-affinity) state, thus promoting the aggregation process.

Chemical oscillations in closed macromolecular systems.

A cycle of irreversible, first-order, autocatalytic reactions among different states of a polyfunctional macromolecule, subject to the conservation of mass, can display stable chemical oscillations. This introduces a class of nonlinear dynamic models for energy transduction in closed macromolecular systems.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Allosteric interpretation of the oxygen-binding reaction of human hemoglobin tetramers.

An allosteric model is presented that provides a simple explanation for the low population of triply ligated species, relative to the other species, in the oxygenation of human hemoglobin tetramers as found in high-concentration studies [Gill, S. J., Di Cera, E.

Oxygen binding constants for human hemoglobin tetramers.

High-precision studies of oxygen binding in hemoglobin (HbA0) solutions at near-physiological concentrations (2-12 mM heme; pHs 7.0-9.1; various buffers) have led to an unanticipated result: an unmeasurably low contribution from the triply ligated species.

Cooperative free energies for nested allosteric models as applied to human hemoglobin.

A model is developed for ligand binding to human hemoglobin that describes the detailed cooperative free-energies for each of the ten different ligated (cyanomet) species as observed by Smith and Ackers (Smith, F.R., and G.

Discrimination of tertiary and quaternary Bohr effect in the O2 binding of Helix pomatia beta-hemocyanin.

Simultaneous determination of proton uptake and oxygen binding has been carried out on Helix pomatia beta-hemocyanin under equilibrium conditions in the absence of buffer and at different initial pH values. Oxygen-binding isotherms of unbuffered H. pomatia beta-hemocyanin, in the presence of phenol red as pH indicator, have been determined employing a thin-layer apparatus.

A cooperative model for ligand binding to biological macromolecules as applied to oxygen carriers.

This paper presents a model describing the thermodynamics of cooperative ligand binding to multimeric biological macromolecules and integrating some of the features of the two-state and induced-fit models. The protein is taken to be partitioned into a number of noninteracting functional constellations, each one existing in two possible quaternary conformations. Furthermore, the model postulates that a functional constellation is organized in several subsets of sites (called cooperons), in which subunits interact according to an induced-fit mechanism.