Phosphatidylinositol-specific phospholipase C in fetal membranes and uterine decidua.
An assay procedure was developed in which phosphatidyl[2-(3)H]inositol was employed as substrate for the measurement of phosphatidylinositol-specific phospholipase C activity. Employing this assay, phosphatidylinositol-specific phospholipase C activity in human fetal membranes and uterine decidua was identified and characterized. The specific activity of this enzyme in amnion (4.4 mumol x mg(-1) protein x h(-1)) was three times that in uterine decidua and more than five times that in chorion laeve. No difference was found between the specific activity of phosphatidylinositol-specific phospholipase C in placental amnion and that in reflected amnion. The products of phosphatidylinositol hydrolysis in short-term incubations were stoichiometric amounts of diacylglycerol and inositol-1,2-cyclic-phosphate plus inositol-1-phosphate. After longer periods of incubation, monoacylglycerol also was detected. Diacylglycerol lipase activity also was demonstrated in these tissues. More than 90% of phosphatidylinositol-specific phospholipase C activity of amnion tissue was recovered in the 105,000-g supernatant fraction, and optimal enzymatic activity in vitro was observed at pH 6.5-7.5 in the presence of Ca(2+) (8 mM) and mercaptoethanol (4 mM). Phosphatidylinositol-specific phospholipase C activity was stimulated by fatty acids in low concentrations, but was inhibited by lysophosphatidylcholine and a variety of detergents. No effect of labor on the specific activity of phosphatidylinositol-specific phospholipase C in either fetal membranes or uterine decidua could be detected. The finding of an active phosphatidylinositol-specific phospholipase C activity in human fetal membranes and uterine decidua is complementary to our previous finding of a selective loss of arachidonic acid from phosphatidylinositol of human fetal membranes during labor. The action of phosphatidylinositol-specific phospholipase C, coupled to diacylglycerol lipase action, could provide a mechanism for the release of arachidonic acid for prostaglandin biosynthesis during parturition.
D001095:Arachidonic Acids / Q000096:biosynthesis; D002118:Calcium / Q000494:pharmacology; D003656:Decidua / Q000201:enzymology*; D003902:Detergents / Q000494:pharmacology; D005321:Extraembryonic Membranes / Q000201:enzymology*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007743:Labor, Obstetric; D008049:Lipase / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D011247:Pregnancy; D013347:Subcellular Fractions / Q000201:enzymology; D010738:Type C Phospholipases / Q000378:metabolism*
D001095:Arachidonic Acids; D003902:Detergents; D010716:Phosphatidylinositols; D010740:Phospholipases; D008049:Lipase; D010738:Type C Phospholipases; D002118:Calcium