Dynamics of adsorption of native and alkylated derivatives of bovine serum albumin at air-water interfaces

Daechul Cho, Purdue University

Abstract

The dynamics of adsorption of bovine serum albumin (BSA) and certain surface-modified (methylated or pentylated) derivatives at the air-water interface was investigated through measurements of surface pressure ($\Pi$) and surface concentration ($\Gamma$), via a radiotracer technique. The steady-state values of $\Gamma$ and $\Pi$ ranged from 0.8 to 1.3 mg/m$\sp2$ and from 10 to 17 mN/m, respectively, for bulk concentrations of 0.5 to 10 ppm. These values and the rates of increase were smaller for pentylated BSA than for native BSA. The $\Pi$-$\Gamma$ relationship during adsorption dynamics differ from the surface equation of state obtained with the spread monolayer. The area per adsorbed protein molecule (A) during adsorption is smaller than that for spread monolayer, indicating that the protein molecule is partially unfolded during adsorption. A for pentylated BSA is larger than that for native BSA due to more unfolding of the former because of higher surface hydrophobicity. The steady-state $\Pi$-$\Gamma$ relationship agrees well with the isotherm obtained from the monolayer experiments. Diffusional losses from spread protein monolayers prepared by Trurnit's method are evaluated with new models and are shown to be negligible for irreversible adsorption. A previously developed model (Narsimhan and Uraizee, Biotech. Prog. 8, 187, 1992) was modified to better account for electrostatic energy barrier to adsorption by postulating that the charges are uniformly distributed in an adsorbed protein layer of finite thickness. The predictions of the new model agree better with the data for native and alkylated BSA than the previous model, especially at low ionic strengths. $\Pi$-A isotherms of spread monolayers of BSA mixed with egg-lecithin of different compositions were obtained. Experiments for adsorption of BSA from the bulk solution onto lecithin monolayers of different surface concentrations indicate enhanced rapid initial adsorption of BSA at small times usually followed by gradual desorption at longer times. These results provide useful insights on lipid-protein interactions for possible food and biological applications.

Degree

Ph.D.

Advisors

Franses, Purdue University.

Subject Area

Chemical engineering|Biochemistry

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