Effect of phospholipase A2 on Ca2+-stimulated adenosine triphosphatase activity in microsomal fraction of rat submandibular gland.

The effect of phospholipase A2 on the Ca2+-ATPase (EC 3.6.1.3) activity in the microsomal fraction of rat submandibular gland was kinetically studied in vitro. The Ca2+-ATPase activity was significantly increased by the treatment with phospholipase A2 in the presence of bovine serum albumin as a scavenger for hydrolyzed products. When the microsomal fraction was incubated with phospholipase A2 in the absence of bovine serum albumin, the Ca2+-ATPase activity was not altered. The Vmax and Km values for both ATP and Ca2+ were increased by the phospholipase A2 treatment, respectively. These results indicated that the activation of Ca2+-ATPase by the phospholipase A2 treatment is due to the increase of Vmax.