HYDROLYSIS OF PHOSPHOLIPID MONOLAYERS BY PHOSPHOLIPASE-D AT THE OIL-WATER INTERFACE UNDER THE CONTROL OF THE POTENTIAL DROP ACROSS THE MONOLAYER

A new method has been proposed for measuring the enzymatic hydrolysis of phosphatidylcholine (PC) monolayers formed at the polarized nitrobenzene(NB)/water(W) interface under the precise control of the potential drop across the interface. As a probe for the hydrolysis, the method utilized the capacitance (C(dl)) of the monolayer. Phospholipase D (EC. 3.1.4.4., PLD) converted L-alpha-dipalmitoylphosphatidylcholine (DPPC) in the monolayer to L-alpha-dipalmitoylphosphatidic acid (DPPA), leading to a drastic decrease in C(dl). This change in C(dl) was sensitive enough to monitor the course of enzymatic hydrolysis of the PC monolayer by PLD. The rate of the hydrolysis was markedly dependent on the potential drop across the interface. When the potential of the aqueous phase with respect to that of the NB phase (DELTA-0W-phi) was -140 mV, no hydrolysis was observed, whereas at DELTA-0W-phi = 60 mV the hydrolysis proceeded promptly.