CHEMICAL MODIFICATION OF CRYSTALLINE ULTRAFILTRATION MEMBRANES AND IMMOBILIZATION OF MACROMOLECULES

Crystalline bacterial cell surface layers (S-layers) from Bacillus stearothermophilus were used for the production of ultrafiltration membranes. The active filtration layer consists of S-layer fragments which are composed of identical protein subunits. S-layer ultrafiltration membranes were found to possess a net negative surface charge due to the presence of free carboxyl groups exposed on the protein domains and in the pore areas. For chemical modification, carboxyl groups were activated with carbodiimide, and could then react with the amino groups of low molecular weight molecules of different size and structure. Modified S-layer ultrafiltration membranes generally showed a very low protein adsorption. Depending on the molecular size and structure of the covalently attached molecules myoglobin (MW 17,000) and/or carbonic anhydrase (MW 30,000), rejection was increased in comparison with non-modified membranes. Carbodiimide-activated carboxyl groups were also used for immobilizing macromolecules such as invertase (MW 270,000) or glucose oxidase (MW 150,000). Both proteins were bound with a very dense packing order, generating an enzyme monolayer on the crystalline S-layer matrix.