Fractions (5 mL) were collected and tested for peptidase activity (see Section 2.7.1). Active fractions were pooled and dialysed (100-fold volume; cellulose membrane, 14 kDa cut-off) against buffer C (10 mm MOPS buffer, pH 6.5, 1 mm CaCl2) at 4–6 °C for 24 h, including one buffer exchange.