Effect of Phospholipase A₂on the Activity of Cabbage Phospholipase D

Abstract

ABSTRACT. As a model study for in vivo interplay between phospholipase D(PLD) and phospholipase A2(PLA2), effect of PLA2 on the activity of cabbage PLD was examined employing phosphatidylcholine(PC) small unilamellar vesicles(SUV). The PLD activity was inhibited in the presence of PLA2. Almost complete inhibition of PLD activity could be brought about with increasing amount of PLA2. In order to evaluate the inhibitory effect of PLA2, effects of its products LPC and oleate were examined by adding individually to the SUV. The exogenously added oleate enhanced the PLD activity, while the LPC inhibited the PLD activity. However, in combination of LPC and oleate, the PLD activity was inhibited as similariy to the PLA2 added directly to the assay system. The oleate enhancement effect was greater than the other saturated fatty acids examined. The inhibitory effect of LPC was also extended to other lysophospholipids. Among the lysophospholipids tested here, all except LPA inhibited the PLD activity. LPA showed marked activational effect. The modulational effect of the molecules produced by PLA2 on the PLD activity was further investigated by examining the stability of bilayer structure and the size of mixed vesicles in addition to carrying out the kinetics of Michaelis-Menten. The results presented here could show a possibility of in vivo clue for the modulation of PLD activity by the products of PLA2 under the certain experimental conditions.