Effects of Secretory PLA₂ on Rat Peritoneal Mast Cells Activated by Different Secretagogues

Abstract

Phospholipase A₂ (PLA₂) is a family of enzymes which releases lysophospholipids and free fatty acids by catalyzing the hydrolysis of the acyl ester bond at the sn-2 position of phospholipid molecules. Arachidonic acid released by PLA₂ from mammalian cells is then further metabolized by cyclooxgenase or lipoxygenase to form eicosanoids. At least three mammalian PLA₂ have been identified:¹ two are 14-kDa secretory enzymes and one is an 85-kDa in-tracellular enzyme. The two secretory PLA₂s are structurally different and are categorised as type I (sPLA₂-I) and type II (sPLA₂-II). The type I enzyme is most abundant in the mammalian pancreas and has long been considered to function solely as a digestive enzyme. However, recent identification of this enzyme in non-digestive organs suggested that it may play a role in cell proliferation and in smooth muscle contraction.² The concentration of sPLA₂-II is increased in synovial fluids and plasma of patients with diverse inflammatory diseases.³ The sPLA₂-II may hence play important roles in the pathogenesis of these inflammatory diseases.