Chemically modified glucose oxidase with enhanced hydrophobicity: Adsorption at polystyrene, silica, and silica coated by lipid monolayers

Covalent modification of glucose oxidase from Aspergillus niger by the palm itic acid ester of N-hydroxysuccinimide at a molar ratio ester:protein of 5 6:1 results in the formation of the enzyme derivative with 11 attached palm itic chains. Surface hydrophobicity measurements by a fluorescent probe, 8- anilino-1-naphthale-nesulfonate, indicate a drastic increase in the hydroph obicity index of glucose oxidase after such a modification. The modified gl ucose oxidase displays a much higher adsorption affinity for hydrophilic (s ilica) as well as for hydrophobic (silica coated by phosphatidyl choline an d cholesterol monolayers and polystyrene latex beads) surfaces, and forms m ore compact surface layers compared to the native glucose oxidase. Such a d ifference results from a spontaneous formation of micelle-like aggregates ( clusters) of the hydrophobized enzyme molecules (average size 500 nn), whic h come into contact with a surface. A possible structure of the glucose oxi dase surface layers and the nature of the forces determining the adsorption of the enzyme on various adsorbents are discussed. (C) 1999 Academic Press .