Initiation of human parturition. X. Substrate specificity of phospholipase A2 in human fetal membranes.

The substrate specificity of phospholipase A acitivty of fetal membranes and uterine decidua was investigated with the use of synthetic substrates, and emphasis was on the specificity of fatty acid esters in the sn-2 position of glycerophospholipids. Rat liver mitochondria were also used as an enzyme source for the substrate specificity studies. Phosphatidylethanolamine was found to be hydrolyzed more rapidly than was phosphatidycholine by the phospholipase A activities of human fetal membranes and uterine decidua and of rat liver mitochondria. The phopholipase A2 in fetal membranes preferentially effected the hydrolysis of phosphatidylethanolamines containing specific fatty acids in the sn-2 position in the following order: arachidonic acid greater than oleic acid less than palmitic acid. No remarkable specificity for arachidonyl esters in the sn-2 position of phosphatidylethanolamines was observed for the phospholipase A activities of human uterine decidua or rat liver mitochondria. The results of this study are consistent with the view that human fetal membrane phospholipase A2 that preferentially hydrolyzes the phosphatidylethanolamines that contain arachidonic acid in the sn-2 position is, in part, responsible for the highly selective accumulation of free arachidonic acid in the amniotic fluid of women in labor.