Properties of Protein Adsorption and Desorption of Alumina Ceramic Membrane.

Abstract

The properties of protein adsorption and desorption of alumina ceramic membranes were investigated using several types of proteins. The effect of pH on the protein adsorption was studied by soaking the membrane in protein solution. For basic proteins, the amount of protein adsorbed increased at pHS Iower than the isoelectric point due to an electrostatic interaction between the protein and the membrane. A single protein solution was filtered and the protein was adsorbed on the membrane. Most of the adsorbed protein was desorbed and conceutrated by changing the ionic strength or pH of the filtered solvent, however, the protein remaining on the membrane was not washed out even by soaking in sodium lauryl sulfate (SDS) solution. The adsorption-desorption experiments were carried out using a binary protein solution of lysozyme and p-galactosidase of pH 3 for the adsorption step and phosphate buffer solution of pH 7 for the desorption step. During the adsorption step, P-galactosidase was adsorbed more than the lysozyme, however, the absolute adsorbed amount was smaller than that in the single protein solution of P-galactosidase since the adsorption site was partially occupied by lysozyme. P-Galactosidase was concentrated seven-fold in the permeate during the desorption step in the first 20 s, while the concentration of lysozyme was one-tenth of its original value.Keywords: protein adsorption, protein desorption, ceramrc membrane mrcrofiltratron Protein adsorption and desorption are important subjects during ultrafiltration and microfiltration processes. For ultrafiltration, the protein itself is usually a separation target and rejected protein is adsorbed on the membrane surface using lower-molecular-weight cut-off membranes (Matthiasson, 1983, Turker & Hubble, 1987 or partially permeable membranes (Fane et al, 1983). Most polymeric membranes are negatively charged in the range of pH 3 to 7, and the adsorbed amount of protein (BSA) increased as the pH decreased in the region below the isoelectric point because of an electrostatic interaction between the protein and membrane surface (Matthiasson, 1983, Turker & Hubble, 1987. In another paper, the maximum adsorption was observed at the isoelectric point due to a weakness of the repulsive interaction between BSA molecules (Fane et al, 1983). For the microfiltration membrane, Bowen and Gan (1990) studied the adsorption properties of BSA on a hydrophilic polyvinylldene fiuoride (PVDF) membrane. In this case, both of the protein-membrane and protein-protein interactions were observed. The maximum adsorbed amount of protein (0.2-0.4 mg'm~2) was obtained in the region of the isoelectric point, pH 4.9. The minimum point was observed at around pH 4, and at lower pHs, the adsorbed amount of protein increased again. Persson et al ( 1993) studied the adsorption properties of ~-lactoglobulin on four kinds of organic membranes made of nylon-66, cellulose acetate, and hydrophilic and hydrophobic types of PVDF. The adsorption amount using a hydrophilic PVDF membrane was the least, al...