(a) SDS-PAGE of glutaraldehyde-crosslinked cysC, showing purification of monomers from oligomers. Lane 1: Chitin column elution. Lane 2: Concentration by 3 kDa ultrafiltration. Lane 3: Filtrate of 30 kDa ultrafiltration. Lane 4: Concentration of filtrate of lane 3 by 3 kDa ultrafiltration. Lane 5: Retentate of 30 kDa ultrafiltration. Each lane contains 2.5 μg total protein. (b) Comparison of reducing and non-reducing conditions. Lane 1: Filtrate (monomer-rich) fraction, reduced and boiled. Lane 2: Filtrate (monomer-rich) fraction, non-reduced, not boiled. Lane 3: Retentate (oligomer-rich) fraction, reduced and boiled. Lane 4: Retentate (oligomer-rich) fraction, non-reduced and not boiled. Each lane contains 3 μg total protein.