Reviewing the thermodynamic parameters characterizing self-association and ligand binding of proteins at 25 OC, we find AGO, AHo, AS\", and ACpo are often all of negative sign. It is thus not possible to account for the stability of association complexes of proteins on the basis of hydrophobic interactions alone. We present a conceptual model of protein association consisting of two steps: the mutual penetration of hydration layers causing disordering of the solvent followed by further short-range interactions. The net AGO for the complete association process is primarily determined by the positive entropy change accompanying the first step and the negative enthalpy change of the second step. On the basis of the thermochemical behavior of small molecule interactions, we conclude that the strengthening of hydrogen bonds in the I n the past decade, a complete thermodynamic description of the self-association of many proteins and their interactions From the Laboratory of Molecular Biology (P.D.R.) and Laboratory of Nutrition and Endocrinology (S.S.), National Institute of Arthritis, Metabolism and Digestive Diseases, National Institutes of Health, Bethesda, Maryland 20205. Received September 23, 1980. low dielectric macromolecular interior and van der Waals' interactions introduced as a consequence of the hydrophobic effect are the most important factors contributing to the observed negative values of AHo and ASo and hence to the stability of protein association complexes. The X-ray crystallographic structures of these complexes are consonant with this analysis. The tendency for protein association reactions to become entropy dominated and/or entropy-enthalpy assisted at low temperatures and enthalpy dominated at high temperatures (a consequence of the typically negative values of AC,\") arises from the diminution of the hydrophobic effect with increasing temperature which is a general property of the solvent, water. with small molecular substrates has become available. Concomitantly, X-ray crystallography has provided a detailed picture of some of these associations, and this has stimulated a number of theoretical studies (Levitt & Warshel, 1975; Gelin & Karplus, 1975; Chothia & Janin, 1975), based upon energetic considerations, to account for these structures. The This article not subject to U S . Copyright. Published 1981 by the American Chemical Society T H E R M O D Y N A M I C S O F P R O T E I N A S S O C I A T I O N V O L . 2 0 , N O . 1 1 , 1 9 8 1 3097 Table I: Thermodynamics of Protein Association' association process A G \" ~ AiY A s o , A c p o (kcal mol-') (kcal mol-l) (cal K-I mol-') (cal K-I mol-I) refb trypsin (bovine) + inhibitor (soybean) -14.6 8.6 78 -440 c, d deoxyhemoglobin S gelation -3.4 2.0 18 -200 e, f lysozyme self-association (indefinite) -3.9 -6 .4 -8.3 g glucagon trimerization -12.1 -3 1 -64 -430 h, i hemoglobin t haptoglobin -11.5 -3 3 -7 3 -940 i a-chymotrypsin dimerization -7.1 -35 -9 5 k, I S-peptide + S-protein (ribonuclease) -13 -40 -90 -1100 m, n All thermodynamic parameters expressed per mole of complex formed except the indefinite association cases of hemoglobin S and lysozyme for which the mole refers to the monomeric protein reacted. Unitary entropy and free energy are given for processes of defined stoichiometry. Standard states are hypothetical 1 M protein, pH at which the reaction was measured. All pHs were close to 7 except for trypsin, pH 5, haptoglobin, pH 5.5, and glucagon, pH 10.5. All data for 25 \"C except glucagon, T = 30 \"C. ence is to calorimetric work and the second is to X-ray crystallographic structure determination. al. (1974). e Rosset al. (1977). Wishner e t al. (1975). g Banerjee et al. (1975). Johnson et al. (1979). * Sasaki et al. (1975). For each entry, the first referSweet et Baugh & Trowbridge (1972). Lavialle et al. (1974). Shiao & Sturtevant (1969). lVandlen &Tulinsky (1973). Hearn et al. (1971). Wyckoff e t al. (1970). methodology and problems involved in such calculations have been critically reviewed by NBmethy & Scheraga (1977). In this paper we review the thermodynamics of protein association processes for the examples best characterized in terms of their chemistry and structure. From this survey we find that the thermodynamic parameters AGO, Ai?, AS\", and ACpo are predominantly of negative sign. This result poses severe difficulties for interpretations of protein association based upon the entropically driven hydrophobic effect. The aim of this paper is to attempt to account for the signs and magnitudes of these thermodynamic parameters for protein association reactions in terms of known molecular forces and the thermochemistry of small molecule interactions.

Thermodynamics of protein association reactions: forces contributing to stability

Isothermal titration calorimetry

1. 1. Some properties of haemoglobin isolated from larval haemolymph of the dipterian family Chironomidae are described in the light of the historical accumulation of our knowledge and recent findings, and on the broad basis of the comparison with haemoglobins from other invertebrates as well as from other chosen vertebrate species. 2. 2. The possible evolutionary connections of these Hbs with the whole family of the haem proteins are demonstrated and it is concluded that almost the same functional properties can be realized by different primary structure of proteins and vice versa . This means that we are able to find some important amino acid blocks or other structural relations characteristic for Hb in other globular proteins. 3. 3. Particular attention is devoted to the relationship between structure and function of these proteins, especially the structural and dynamical conditions of the Bohr effect and a high oxygen affinity. 4. 4. The adaptative significance of haemoglobins to the Chironomids' larvae in mud habitats is discussed in relation to their function. The double role of these Hbs is shown: they can act as a short time oxygen store (connected with the larval respiratory behaviour) and an oxygen transferer (connected with the metamery of the larvae). It is also suggested that they may play an important role in some detoxification processes.

Structure, function and physiological role of chironomus haemoglobin

Proton nuclear nagnetic resonance characterization of heme disorder in monomeric insect hemoglobins.

An empirical extremum principle for the hill coefficient in ligand-protein interactions showing negative cooperativity

Analysis of ligand binding curves in terms of species fractions

Thermodynamics of ligand-binding and allosteric transition in hemoglobins - reaction of hb-trout-iv with co

A calorimetric study has been made of the heats of CO reaction with the monomeric haemoglobins of Chironomus thummi thummi III and IV as a function of pH. The number of Bohr protons released at pH 7.1 was determined from heats of reaction in different buffers as 0.19 and 0.31 mot H+/mol CO for haemoglobin III and IV respectively. The heat of the Bohr ionization process was found to be 6 and 8 kcal/mol H+ (25 and 34 kJ/mol) for the haemoglobins III and IV. These values are consistent with values found for histidine groups. A pH-independent part of the reaction enthalpy was determined as - 19.7 kcal/mol CO (- 82.4 kJ/mol). The same reaction with myoglobin is less exothermic. From the combination of ΔG° and ΔH° values TΔG° values have been calculated. It was found for both haemoglobins that the entropy of reaction is greater by 2 cal K-1 mol-1 (8.4 J K-1 mol -1) at pH 9.5 as compared to pH 6.0.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1976.tb10192.x

A calorimetric study of the CO Bohr effect of monomeric haemoglobins.

The heat of reaction of CO gas with the alpha2Mmetbeta2 and alpha2Mbeta2 species of the alpha-chain mutant hemoglobin M Iwate has been studied in buffers with different heats of ionization of 25degrees and in the absence of organic phosphates. For the alpha2Mmetbeta2deoxy species we find a small Bohr effect (0.12 mol of H+/mol of CO) which is in correspondence with that found in equilibrium studies. The heat of reaction, when corrected for proton reaction with buffer, is -18.4 +/- 0.3 kcal/mol of CO at pH 7.4 At pH 9 the same value is observed within experimental error. This value compares closely with heats of reaction of CO with myoglobin and with van't Hoff determinations of the heat of oxygen binding to isolated hemoglobin alpha and beta chains after correction for the heat of replacement of O2 by CO. Furthermore, an analysis of the differential heat of ligand binding as a function of the extent of reaction indicated that, within experimental error, the heat of reaction with the first beta-chain heme in alpha2Mmetbeta2deoxy is the same as the second. Since the quaternary Tleads to R transition is blocked in this mutant hemoglobin, we compared it with Hb A to estimate the enthalpic component of the allosteric T leads to R transition in Hb A. The heats of reaction with CO(g) and Hb A are -15.7 +/- 0.5 and -20.9 +/- 0.5 kcal/mol at pH 7.4 and 9.0, respectively. In going from the T to the R state we find an enthalpy of transition of 9 +/- 2.5 kcal at pH 7.4 and -12 +/- 2.5 kcal at pH 9.0. From published free energies of transsition we conclude the T leads to R transition is enthalpically controlled at p/ 7.4 but entropically controlled at pH 9.0 A near normal Bohr effect is estimated from heats of reaction of CO with alpha2Mdeoxybeta2deoxy in various buffers. A large than normal heat of reaction (-21.6 +/- 0.5 kcal/mol of CO) is attributed to the abnormal alpha chains in Hb M Iwate.

H.T. Gaud

Papers

Analysis of ligand binding curves in terms of species fractions

Thermodynamics of ligand-binding and allosteric transition in hemoglobins - reaction of hb-trout-iv with co

A calorimetric study of the CO Bohr effect of monomeric haemoglobins.

Heats of carbon monoxide binding by hemoglobin M Iwate.

Enthalpy changes for hemoglobin-ligand interactions: Revised calorimetric data