HYDROLYTIC ACTIVITY OF PHOSPHOLIPASE-D FROM PLANTS AND STREPTOMYCES SPP AGAINST PHOSPHATIDYLCHOLINE MONOLAYERS AT THE POLARIZED OIL-WATER INTERFACE

A previously proposed method of measuring phospholipase D (PLD) activity using the change in electrical capacitance of a phospholipid monolayer at the polarized oil/water interface has been applied, with some modifications, to a comparative study of the hydrolytic activity of four PLDs frequently used in transphosphatidylation. Distinctive differences in the activities of PLDs from Streptomyces spp. and PLDs from plants were revealed. The two PLDs from Streptomyces spp. hydrolyzed the monolayer completely, whereas peanut and cabbage PLDs hydrolyzed up to 75% and 60% of the monolayer respectively. Peanut PLD did not show an absolute requirement for Ca2+, whereas the hydrolytic activity of S. chromofuscus PLD was appreciably enhanced at 50 mM Ca2+. The rate of hydrolysis for PLDs from plants showed little dependence on interfacial potential, while the rate for PLDs from Streptomyces spp. was highest when the potential of the aqueous phase was -90 mV relative to that of the oil phase. The Frumkin two-parallel-plate condenser model for the adsorption of PLD provided a good description of the observed potential-dependent activity of PLD.