Protonation of Lysozymes and Its Consequences for the Adsorption onto a Mica Surface

Abstract

Several physicochemical properties of chicken egg white lysozyme (LSZ) in electrolyte solutions were determined. The hydrodynamic diameter of LSZ at an ionic strength of 0.15 M was found to be 4.0 nm. Using the determined parameters, the number of uncompensated (electrokinetic) charges, N(c), on the molecule surface was calculated from the electrophoretic mobility data. It was found that the N(c) = 2.8 at pH = 3.0 and an ionic strength of I = 0.15 M. At the lower ionic strength, I = 1 × 10(-3) M, this positive charge increased to N(c) = 5.6 at a pH = 3.0 The physicochemical characteristics were supplemented by the dynamic viscosity measurements. The intrinsic viscosity and the hydrodynamic diameter results were compared with theoretical predictions from Brenner's model. Using this approach, it was found that the effective molecule length of LSZ is equal to L(ef) = 5.6 nm. Additional information on the LSZ adsorbed films was obtained by the contact angle measurements. The notably large contact angles were measured on LSZ films formed under the conditions where both the LSZ and the mica were oppositely charged. The higher the positive zeta potential of LSZ, the greater the contact angle measured, which indicates that LSZ affinity for the adsorption on mica increases with its uncompensated charge. The adsorption dependence on the zeta potential of LSZ was explained, assuming a roughly uniform distribution of the net charge on the molecule surface. This assumption is supported by the results of depositing negatively charged, fluorescent latex particles onto the mica surface, which had been modified by LSZ adsorption. The highest latex coverage was formed on mica surfaces that had first been coated with LSZ solutions of lower pH, as a result of the increasing charge of LSZ monolayers in this condition.

Lysozyme adsorption at a silica surface using simulation and experiment: effects of pH on protein layer structure

“…On the basis of these measurements the zeta potential of the protein solutions was calculated, depending on the pH. 18 …”

“…18,19 Several measurements were taken for the silica surfaces and the average value determined. All measurements were performed at 295 K.…”

Structure, orientation and stability of lysozyme confined in layered materials

“…41,42 The kinetics of lysozyme adsorption on different layered materials are depicted in Fig. Under these conditions, the protein is globally positively charged.…”

Stability of silver nanoparticle monolayers determined by in situ streaming potential measurements

“…This is a rather unusual behavior, contradicting the mean-field DLVO theory, because negatively charged particles are deposited on negatively charged (on average) substrate. However, such deviations were often observed for colloid particle adsorption on protein supporting layers, e.g., fibrinogen (Adamczyk et al 2011a) and albumin (Jachimska et al 2012). They were quantitatively explained in terms of the heterogeneous charge distribution in the supporting layer stemming from molecule density fluctuations.…”