Enrico Di Cera

Effect of temperature on oxygen affinity and anion binding of bovine hemoglobin

Measurements of oxygen binding to bovine hemoglobin have been carried out over the temperature range 15-37 degrees C at pH 7.33. The standard enthalpy of oxygenation after correction for the heat of oxygen solution and of the Bohr protons is found to be -7.1 or -7.2 kcal/mol in the presence of 0.1 M chloride or bromide, respectively. This value is well below the -14.4 kcal/mol determined for human hemoglobin under identical experimental conditions. As reported by Fronticelli et al. (C. Fronticelli, E. Bucci and A. Razynska, J. Mol. Biol. 202 (1988) 343), the preferential binding of anions by bovine hemoglobin recognizes the various halides. Measurements at various temperatures reveal that this is true only above 25 degrees C. The halide recognition and the less exothermic enthalpy of oxygenation of bovine hemoglobin are probable due to oxygen-linked hydrophobic effects that are larger in bovine than in human hemoglobin.

INHIBITION OF FIBRINOGEN BINDING TO HUMAN-PLATELETS BY BLOCKAGE OF NA+/H+ EXCHANGE.

Binding of ADP to platelets enhances the binding of fibrinogen to Gp IIb-IIIa, the specific platelet receptor for adhesive proteins. The linkage between ADP and fibrinogen binding is indirect since ADP does not bind to the same receptor as fibrinogen. We have recently proposed that a third component, once affected by ADP binding, induces a conformational transition of the fibrinogen receptor from the low to the high affinity state, which is responsible for platelet aggregation [De Cristofaro, R., Landolfi, R., Castagnola, M., De Candia, E., Di Cera, E., & Wyman, J. (1988) Proc. Natl. Acad. Sci. USA 85, 8473-8476]. In the present study we provide evidence that this component should be identified with the platelet Na+/H+ antiport. Inhibition of the antiport by pharmacological agents such as amiloride, or else by decreasing extracellular Na+, results in a marked decrease of fibrinogen binding to platelets.

Negative binding capacity and bistability in one‐component systems

The apparent violation of the second law at the level of individual site binding phenomena in a biological macromolecule working as an enzyme is shown to induce bistability in a simple one‐component system.

Information theory and the analysis of ligand-binding data

The phenomenological principles of information theory are used in the analysis of ligand-binding phenomena in biological macromolecules. Information maps are constructed to visualize regions of ligand chemical potential with maximum amount of information and to devise suitable experimental strategies therefrom. Extensive simulation studies and analysis of experimental data also point out the properties of information used as a weighting procedure in nonlinear least-squares analyses.

Linkage as process and paradox

Abstract Linkage in equilibrium and far from equilibrium systems is discussed in terms of process and paradox. The process complies with the reciprocity of effects, chemical or physical. The paradox arises when dealing with particular aspects that seem to be relevant for biological systems.

Point perturbation analysis of experimental data.

A new method of data analysis is proposed. The method is based on discrete perturbation of experimental data points, which is used to probe the metric of the parameter hyperspace. Perturbation-induced fluctuations in the residual values are analysed by discrete Fourier transform to yield the autocorrelation function and a relaxation length for each experimental point. This parameter provides a quantitative measure of correlation and hence nonrandomness of residuals. The method is applied to the analysis of measurements of the shear viscosity of a 2,6-lutidine/water mixture near the critical point, and to the oxygen and carbon monoxide binding reactions to human hemoglobin. Relaxation profiles are constructed for several experimental data sets. Departure from random behavior in the residuals is discussed in connection with the theoretical interpretations of the phenomenon under consideration.

The linkage between adenosine nucleotide binding and amidase activity in human α-thrombin

Abstract The amidase activity of human α-thrombin has been studied in the presence of the adenosine nucleotides AMP, ADP and ATP. At low concentrations, adenosine nucleotides increase thrombin activity tip to 30%, while at high concentrations (5 mM) inhibition takes place up to 20%. Inhibition is progressively reduced by increasing substrate concentration. A simple, phenomenological description of the linkage between adenosine nucleotide binding and amidase activity of human α-thrombin is proposed and the free energy changes for the underlying reactions involved in the linkage scheme are resolved by global analysis of the experimental data. The linkage scheme assumes that thrombin activation is determined by a conformational transition due to binding of adenosine nucleotides to a regulatory site. Inhibition, on the other hand, would be a consequence of competitive binding to the catalytic site.

Birhythmicity and a route to turbulence through limit cycle fusion in a simple autocatalytic system

Abstract A simple system of autocatalytic reactions shows bistability, birhythmicity, and a route to turbulence through “fusion” of two independent limit cycles.

Point perturbation analysis of experimental data: II. The statistics of relaxation length values of pseudo-random errors.

The statistics of relaxation lengths for pseudo-random deviates as determined by point perturbation analysis (E. Di Cera, F. Andreasi Bassi and G. Arcovito Biophys. Chem. 34 (1989)239),has been constructed by a Monte Carlo study. The values of the relaxation length, L, approximately follow a Gamma distribution. The results allow for a statistical estimation of relaxation profiles and provide a test for randonmess of residuals which is more accurate than other standard procedures.

Linkage effects in a model for cell survival after radiation

A thermodynamic treatment for the effects of radiation on cell survival is proposed. The treatment is an extension of the linear-quadratic model (K.H. Chadwick and H.P. Leenhouts, Phys. Med. Biol. 13 (1973) 78) following the principles of linkage thermodynamics (E. Di Cera, S.J. Gill and J. Wyman, Proc. Natl. Acad. Sci. U.S.A. 85 (1988) 5077). Linkage effects between chemical binding to DNA and radiation action are considered, along with the synergism between different types of radiations. A simple mathematical condition is found for the additivity of radiation doses that result in an isoeffect. The resolvability of the model parameter is investigated by simulations and statistical analysis of the distributions obtained.