Large solutes induce structural perturbations in proteins and membranes

Abstract

Structural perturbations in biopolymers with hydrophobic interiors i.e. specific proteins and dimyristoylphosphatidylcholine (DMPC) vesicles were investigated as a function of solute concentrations in the medium. 1,6-diphenyl-1,3,5-hexatriene (DPH) was used as fluorescent probe. Response of DPH was comparable to that of intrinsic tryptophan in BSA in terms of steady state and time resolved fluorescence. The solutes induced a decrease in steady state anisotropy as well as rotational correlation time (computed from lifetime measurements) for DPH in both proteins and membranes. Enhanced access of the quencher potassium iodide to tryptophan in bovine serum albumin (BSA) and ovalbumin, and enhanced terbium leakage in DMPC vesicles induced by various solutes concomitant with decreased anisotropy/correlation time were consistent with structural perturbations of the nature of defects or voids in these polymers.