For the improvement of the storage stability and thermostability and for the preparation of water-soluble, enzymatically active conjugates with greater molar masses for use in membrane reactors, the enzymes trypsin, peroxidase and aminoacylase were bound covalently to a water-soluble copolymer of N-vinylpyrrolidinone-2 and acrylic acid. A trypsin-containing conjugate (with 40.6 wt.% of trypsin, a relative activity of 36% and a molar mass of 104,000 D) was succesfully used in continuous and discontinuous membrane reactors.