The oil-drop tensiometer: potential applications for studying the kinetics of (phospho)lipase action

Abstract In 1987, Nury et al. adapted the well-known oil-drop technique for measuring interfacial tension for the purpose of monitoring the lipase hydrolysis of natural long-chain triacylglycerols. On the basis of this initial study, we developed an automated, digitised, computer-driven device with which we further prospected for applications of the oil-drop tensiometer in studies on lipolytic enzyme kinetics. In the present study, we first established that the new device provided reliable interfacial tension measurements, similar to those previously published. Furthermore, by keeping the oil-water interfacial tension at a fixed end-point value, the enzyme kinetics can be monitored using the change with time in the area of the oil drop. We then describe specific applications involving: (i) the measurement of lipase kinetics using minute amounts of enzyme; we checked the existence of a linear relationship between the initial decrease in the interfacial tension and the lipase concentration and found that the initial rates did not vary significantly between several successive drops formed within a 20-min period in the same lipase solution; (ii) the kinetic assay of phospholipase A 2 and (iii) studying the effects of high-pressure conditions upon lipase activity.