PROBABLE PARTICIPATION OF PHOSPHOLIPASE A(2) REACTION IN THE PROCESS OF FERTILIZATION-INDUCED ACTIVATION OF SEA-URCHIN EGGS

In sea urchin eggs activated by sperm, A23187 or melittin, BPB (4-brom ophenacyl bromide, a phospholipase A(2) inhibitor) blocked fertilizati on envelope formation and transient CN--insensitive respiration in a c oncentration-dependent manner. BPB had virtually no effect or th incre ase in [Ca2+](i) (cytosolic Ca2+ level), the activity of phosphorylase a and the rate of protein synthesis, as well as acid production and a ugmentation of CN--sensitive respiration. BPB also inhibited fertiliza tion envelope formation and augmentation of CN--insensitive respiratio n induced by melittin. Melittin, known to be an activator of phospholi pase A(2), induced the envelope formation, acid production, augmentati on oi CN--insensitive and sensitive respiration, but did not cause any increase in [Ca2+](i), the phosphorylase a activity and the rate of p rotein synthesis. An activation of phospholipase A(2) induced by Ca2or melittin seems to result in cortical vesicle discharge and producti on of fatty acids, which are to be utilized in CN--insensitive lipid p eroxidase reactions. Activation of other examined cell functions in eg gs activated by sperm or A23187, probably results from Ca2+-triggered sequential reactions other than Ca2+-caused activation of phospholipas e A(2).