Peptide materials such as enzymes and enzyme inhibitors are rendered water-insoluble by binding the peptide materials to a cross-linked copolymer formed by copolymerizing the following units: (A) about 0.1 to 50 weight percent of at least one Alpha , Beta -monoolefinically unsaturated dicarboxylic acid anhydride having about 4 to 9 carbon atoms and (B) about 99.9 to 50 weight percent of at least one di- and/or poly(meth) acrylate of a diol and/or a polyol.