Amphipathic enzyme—polymer conjugates

Abstract

IMMOBILISATION of enzymes on solid supports to give reusable and stabilised catalysts has been studied extensively¹ but the concept of chemically modifying a water-soluble enzyme to enable its activity to be utilised in the form of a water-immiscible liquid phase has received little attention. Potential advantages of liquid-phase immobilisation include ease of continuous operation, freedom from the effects of solid particle breakdown and the possibility of enhanced activity against water-insoluble liquid substrates. Although the effects of detergent-protein association on protein ex-tractability into iso-octane have been studied² and considerable effort has been expended on the liquid membrane entrapment concept^3,4, another possible type of liquid-phase immobilised enzyme system seems to have been neglected. The latter comprises droplets of a water-immiscible liquid bearing a surface layer of modified enzyme. We have found that some enzymes may be converted into surface-active amphipathic conjugates by covalent coupling to certain types of polymeric detergents (polysoaps) and that the resulting conjugates may bind sufficiently strongly to dispersed water-immiscible liquids to give an enzymatically active emulsion that can be handled as a quasi-liquid phase. The amphipathic enzyme conjugates are analogous to certain membrane-bound proteins such as cytochrome b₅, which have been shown to comprise a hydrophilic protein core anchored to a lipid bilayer by a hydrophobic polypeptide tail^5,6.