Abstract: A membrane is produced by dissolving, in a water-miscible solvent, a water insoluble copolymer of acrylontrile with at least one monomer selected from the group consisting of an aminostyrene, a vinyl pyridine and an N-hydroxy-containing-substituent-acrylamide, casting said solution to form a thin layer of solution, contacting said solution with water thereby to coagulate the copolymer into a film, and washing away from the copolymer film the solution of solvent and water. The amine or hydroxy group of the copolymer is then activated and coupled with a ligand such as glucose isomerase, chymotrypsin or Protein A. The coupled membranes can then be used for biological separations and reactions.