Salt-induced release of lipase from polyelectrolyte complex micelles

Abstract

With the aim to gain insight into the possible applicability of protein-filled polyelectrolyte complex micelles under physiological salt conditions, we studied the behavior of these micelles as a function of salt concentration. The micelles form by electrostatically driven co-assembly from strong cationic block copolymers poly(2-methyl vinyl pyridinium)₄₁-block- poly(ethylene oxide)₂₀₅, weak anionic homopolymers poly(acrylic acid)₁₃₉, and negatively charged lipase molecules. The formation and disintegration of these micelles were studied with dynamic light scattering (DLS), by means of composition and salt titrations, respectively. The latter measurements revealed differences between disintegration of lipase-filled and normal polyelectrolyte complex micelles. These data, together with small angle neutron scattering (SANS) measurements provide indications that lipase is gradually released with increasing salt concentration. From the SANS data a linear relation between the intensity at q = 0 and the volume of the cores of the micelles at different salt concentrations was derived, indicating a loss of volume of the micelles due to the release of lipase molecules. It was estimated that beyond 0.12 M NaCl all lipase molecules are released.