Showing papers on "Cooperative binding published in 1969"

Evidence for histidine in the triethyltin-binding site of rat haemoglobin

Abstract: One molecule of rat haemoglobin binds two molecules of triethyltin. The binding sites are located on the globin and there is co-operativity between the sites such that the intrinsic affinity constant at pH8·0 increases from 3·5×105m−1 for the binding of the first triethyltin molecule to 5·0×105m−1 for the binding of the second. Evidence is presented, from pH studies and the kinetics of inhibition due to photo-oxidation, that each binding site contains two histidine residues.

On the Interaction of Nucleotides with Basic Polyamino Acids. Cooperative Binding Behavior

Abstract: The binding of nucleoside monophosphates by poly-L-arginine and guanosine monophosphate by poly-L-lysine at low ionic strength and pH 7 consists of two phases. At low values of r (number of bound nucleotides per amino acid residue) the binding behavior can be fitted to the Langmuir isotherm; at high r values the binding is cooperative and accompanied by precipitation of a polyamino acid-nucleotide complex. Three different mathematical approaches were used to describe the binding behavior of the cooperative phase. The results indicate that the magnitude of the parameters for nearest neighbor interaction of bound nucleotides parallels the tendency of self-association of the respective bases. A value of about 2 kcal/mole was determined for the nearest neighbor interaction energy of guanosine 5'-phosphate with poly-L-arginine at two different temperatures, and with poly-L-lysine. Two approaches yield intrinsic binding constants which, depending on the model chosen, correspond to binding by sites with free neighbor sites or to direct interaction of nucleotides with the polyamino acid. The intrinsic binding constants obtained with poly-L-arginine depend upon the nature of the nucleotide base and, as is shown in the case of guanosine 5'-phosphate, upon temperature. The corresponding value for guanosine monophosphate with poly-L-lysine is considerably smaller. It is pointed out that interaction of nucleotides with poly-L-arginine may be controlled by both the different stacking tendencies of the nucleotide bases and by the direct affinities between bases and polyamino acid.

Binding of Organic Ions by Proteins

Abstract: Publisher Summary This chapter describes the binding of organic ions by proteins. Although proteins differ with respect to whether they show measurable tendencies to bind small anions, all proteins that have been examined bind large organic anions (the longer-chain fatty acids, ionic detergents, and such aromatic compounds as dyes) to some extent. In general, within a homologous ligand series, the binding affinity increases with the size of the ion. Under some conditions, the binding of these large ions results in precipitation of the complex formed. However, binding and precipitation do not go together in any simple way. The binding of anions by those proteins that have been investigated in detail cannot be expressed as the result of simple multiple equilibria that involve sets of identical binding groups, modified only by the electrostatic effects resulting from changes in charge as the protein interacts with different numbers of ions. These difficulties may be partly because of the fact that detailed ion-binding measurements on soluble proteins have been made on a very small number of proteins.

Metal-Ion Binding

Abstract: Publisher Summary This chapter describes metal–ion binding. Two general classes of proteins are considered for describing metal–ion binding. These are (1) systems in which the metal ion occupies a small number of very high energy sites and is essential for the biological function of the macromolecule (e.g., alkaline phosphatase, carboxypeptidase) and (2) systems in which metal binds reversibly to specific amino acid residues in the polypeptide chain but is not required for biological activity and indeed may even impair protein function or disrupt protein structure. Metal ions, like protons, share electron pairs from the donor atoms of a ligand molecule and, thus, form partially covalent bonds with characteristic heats of formation. This type of binding is distinguished from binding to proteins of neutral molecules or large organic ions such as detergents, where the large binding forces are primarily entropie in origin. All metal ions have sets of characteristic coordination numbers that represent the number of hybrid bonds available for ligands. The binding of metal ions to proteins can be measured by equilibrium dialysis.