Catalytic Properties of Phospholipase D using Phosphatidic Acid as an Activator

Catalytic Properties of Phospholipase D using Phosphatidic Acid as an Activator

The effects of phosphatidic acid(PA) on the activity of phospholipase D were examined in detail. The enzyme activity was examined in the liposome system containing phosphatidylcholine and PA, which was suspended in a desired buffer solution by ultrasonication. The substrate of large unilamella vesicle (LUV) state by ultrasonication was more effective on the enzyme activity than that of multilamella vesicle(MLV) by water-bath type sonication. The most effective molar ratio of PC-PA liposome for enzyme activity was found to be 1:0.7. The other optimum conditions were found 5 mM $Ca^{2+}$ ion, pH 6.6, and incubation temperature of $27^{\circ}C. K_m \;and \;V_{max}$ values were estimated to be 1.43 mM and 0.8 $nmole/min/{\mu}g$ protein respectively. These properties in a PC-PA liposome system were compared with those in a PC-SDS mixed micelle system. The effects of other phospholipids and organic phosphates on the enzyme activity were also examined.