Cell suspension was sonicated for 60 s. with cooling on ice with two cycles of 16 mm using a sonicator (Sonics and Materials Inc., Vibro cell), followed by centrifugation at 9700g for 15 min. The reaction mixture consisted of 180 mL of 0.1 M sodium phosphate buffer, pH 6.0, 10 mL of a 200 mM appropriate conjugated bile salt, 10 mM DTT and 10 mL of cell-free extract.