The models of the denaturation of globular proteins. II. Hydrophobic interactions and conformational transition in polymethacrylic acid

Abstract

SynopsisTo model the compact structures of globular proteins and the processes of their breakdown, the local compact structures have been investigated in the nonionized (or weakly ionized) molecules of polymethacrylic acid (PMA) in aqueous solutions. The potentiometric titration curves differ markedly from the analogous curves for polyacrylic acid (PAA) and show the existence of the cooperative breakdown of the local compact structures in a definite region of the ionization degree. The presence of the local compact structures in the PMA molecules is also manifested in sharp differences between the luminescent characteristics of the dyes (auramine and acridine orange) in aqueous solutions with PMA and the same characteristics in aqueous solutions with PAA. In a certain range (which coincides with the interval of the breakdown of local compact structures) these differences disappear. This permits us to interpret them as the result of the dye molecules binding on the structurized parts of PMA. The assumption has been made that the local compact structures in the PMA molecules in aqueous solutions are stabilized by the hydrophobic interactions of methyl groups. This assumption explains the abnormal temperature dependencies of the properties of the aqueous solutions of PMA and the absence of the local compact structures in the PMA molecules in methanol as well as in the P AA molecules in any solvents. To check this assumption we have. investigated the breakdown of the local compact structures in the PMA molecules when aliphatic alcohols are added to the aqueous PMA solution. It was shown that the transition of dye molecules from the bound state to the free one (which is the evidence of the breakdown of the local compact structures) takes place in the narrow range of alcohol concentrations decreasing in the series methanol-ethanol-propanol-butanol. It means that alcohol destroys compact structures the better, the more hydrophobic groups it possesses.The investigations of intrinsic viscosity of PMA in the water-methanol mixtures have shown that the addition of alcohol leads not only to the breakdown of the local compact structures, but also the unfolding of the macromolecule as a whole. The analogy between the local compact structures in PMA molecules and the compact structures of globular proteins has been discussed.

Binding of Polycarboxylic Acids to Cationic Mixed Micelles: Effects of Polymer Counterion Binding and Polyion Charge Distribution

“…Since PAA is a weak polyelectrolyte whose titratable ionic groups have a pH-dependent degree of ionization (42,43), ␣, we can control the polymer linear charge density ( ) by fixing pH. "Type I" turbidimetric titrations were carried out by adding 40 mM CTAC to 0.50 g/L NaPAA ϩ 20 mM C 12 bidimetrically, corresponds to the onset of polymer-micelle complexation has been verified by dynamic light scattering, electrophoretic light scattering, and fluorescence spectroscopy (44,45).…”

Polyelectrolyte Solutions: Phenomena and Interpretation

“…Since the fluorescence of many dyes is quenched by contact with water, the clustering of PMA around a dye leads to a sharp increase in emission intensity which, as seen in Fig. 5, drops precipitously in the pH range where the pK exhibits a plateau (21). Another evidence for PMA clustering was provided by the reduction of the conformational mobility of binaphthyl residues attached to the polymer chain (22).…”

Resistance of zwitterionic telomers accumulated on metal surfaces against nonspecific adsorption of proteins

“…PMA with a pK a of 6.6 at α (degree of dissociation) = 0.5 [95] is largely ionized at pH 7.0, and is stretched rather than shrunken. The voltammogram for HQ was the same before and after the incubation (data not shown), definitely showing that the disulfide-carrying telomers chemisorbed to the gold surface.…”