USA — Biofunctional membranes: Part IV: In J. MEMBR. SCI. (91/1–2 (47–64) 1994)) D.A. Butterfield, J. Lee, S. Ganapathi and D. Bhattacharyya of the University of Kentucky report on “Biofunctional membranes. Part IV. Active-site structure and stability of an immobilized enzyme, papain, on modified polysulfone membranes studied by electron paramagnetic resonance and kinetics”