Showing papers on "Cooperative binding published in 1971"

A quantitative analysis of proflavine binding to polyadenylic acid, polyuridylic acid, and transfer RNA.

Abstract: Absorbance measurements show that the binding of proflavine to poly (A) and poly(U) can be quantitatively resolved (within ± 10% relative error) by the consideration of two bound species whose spectral properties and mechanisms of interaction are similar to those found in the DNA. proflavin systems: cooperative binding along the phosphate backbone (process I) and interaction between the aromatic rings of base and dye resulting presumably from some kind of interacalation of the ligand between consecutive bases (process II). The comparison with a simple theoretical model shows that process I and process II are not independent but coupled. The spectrophotometric method is able to resolve the binding of proflavine to a tRNA species with the same accuracy as that obtained for poly(A) and poly(U). Accordingly, it is proposed that the mode of interaction between proflavine and all classes of polynucleotides (DNA, RNA, synthetic polymers) is similar in nature. From the differences observed in the distribution of the bound dye between the two complexes, the existence of a close correlation between the secondary structure of the polymer and its ability for binding the dye in complex II is proposed.

The hydration of synthetic polypeptides

Abstract: Water binding isotherms of a series of polypeptide films were measured with the use of a quartz crystal electronic microbalance. The water uptake was found to be proportional to the thickness of the film suggesting that the binding sites are not confined to the surface but are distributed throughout the film. Stoichiometric relationships can be established between the amounts of water uptake and the number of peptide, carboxyl-, and amino groups present in the polypeptide films. The absorption isotherms were interpreted by means of a cooperative binding model which postulates that the binding of water molecules on adjacent sites is facilitated by “next neighbor” interactions. The free energies, heats, and entropies of binding were determined from the temperature dependence of the absorption isotherms. The values obtained were in agreement with those reported in the literature for association processes of water molecules with small molecular weight compounds. Whereas the interaction of water with carboxylic and amino groups could be explained on the basis of hydrogen bond formation, a dipole interaction had to be postulated to account for the binding of water by a-helical peptide groups.

Homotropic cooperative binding of the first component of guinea pig complement to rabbit IgG-erythrocyte complexes: a possible allosteric effect.

Abstract: Binding of the activated first component of guinea pig complement to immune complexes formed between dinitrophenylated erythrocytes and rabbit IgG antibody to 2,4-dinitrophenylhapten has been studied quantitatively. Cooperative binding was observed; it in volves no interactions between the domains on the erythrocyte surface that bind the activated first component of complement, or between the activated complement molecules in solution. By curve-fitting methods, we find that the data are consistent with an allosteric model, which assumes 10 binding sites per domain, a low allosteric equilibrium constant, and virtually exclusive binding to one of the isomers.

The binding of NAD + and NADH to glyceraldehydephosphate dehydrogenase.

Abstract: Publisher Summary This chapter discusses the binding of NAD+ and NADH to glyceraldehydephosphate dehydrogenase. Early studies demonstrated that the rabbit-muscle enzyme binds NAD+ much more firmly than other dehydrogenases, because the crystalline enzyme contains bound NAD+. However, it does not bind NAD+ as firmly as activated charcoal, which completely removes NAD+ from the enzyme. Binding of NAD+ to charcoal-treated enzyme causes the appearance of a broad absorption band with maximum at 360 nm, and the formation of the band is inhibited by iodoacetate or acetyl phosphate. The binding constants of NAD+ to each of the four subunits in the muscle enzymes have been determined by equilibrium dialysis, and using both ultracentrifugation and equilibrium dialysis. This chapter displays the results, given as a Scatchard plot, of the measurements with the lobster enzyme. The curved line, convex to the abscissa, shows that the binding constants become successively less as more NAP becomes bound to the enzyme—that is, there is negative cooperativity. The inset shows that a straight-line Scatchard plot is obtained when the binding of the fourth molecule is plotted on the assumption that the first three sites are completely occupied before NAD+ is bound to the fourth site.

Electron donor‐acceptor complex formation by compounds of biological interest: IV. Complexes of Local Anaesthetics with Electron Acceptors

Abstract: The association constants of benzocaine, procaine, lignocaine and prilocaine with the electron acceptors 1,3,5-trinitrobenzene and 1,4-dicyano-2,3,5,6-tetrafluorobenzene have been determined from NMR chemical-shift measurements. The results have been compared with corresponding constants for complexes of aniline, 2,6-dimethylaniline and 2-methylaniline. For solutions in carbon tetrachloride, unexpectedly high association constants are obtained for the drug molecules compared with the corresponding simple ring-methylated anilines. It is suggested that these results may be due to the cooperative binding by the amino group in the side-chain which increases the overall binding of the drug molecule to the acceptor.