Figure 6

Enzyme activity of outer membrane preparations obtained from cells displaying lipase and foldase. Outer membranes were prepared as described in materials and methods and then applied to an assay with p-nitrophenyl palmitate as substrate and in which the increase of absorption at 405 nm was observed photometrically. The assay was performed in potassium phosphate buffer pH 7.4 at a constant temperature of 25°C. The increase in absorption is caused by the nitrophenylate anion after lipolytic cleavage of the ester bond conducted by the surface displayed lipase. ◯ = outer membrane preparations of E. coli BL21(DE3)pAT-LiFoBc coexpressing both lipase and foldase, ■ = outer membrane preparations of E. coli BL21(DE3) used as control, ☐ = substrate solution in buffer. Mean values with standard deviations are shown, n = 3.