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Evidence of phospho lipase a 2 in the sea urchin lytechinus pictus egg its possible involvement in the cortical granule reaction


Gamete Research 9(3): 329-338
Evidence of phospho lipase a 2 in the sea urchin lytechinus pictus egg its possible involvement in the cortical granule reaction
Fertilization of the sea urchin egg involves an exocytotic event known as the cortical granule reaction (CGR). In many cell systems, phospholipase A2 is implicated in regulation of the secretory event. Phospholipase A2 probably mediates the CGR but there is no direct demonstration of phospholipase A2 activity in the sea urchin egg. We report here evidence of phospholipase A2 activity in egg homogenate of the sea urchin L. pictus. The enzyme was Ca-dependent and had a pH optimum near the intracellular pH of the unfertilized egg. Neither exogenous calmodulin nor trifluoperazine had any apparent effect on enzyme activity. Quinacrine, a phospholipase A12 inhibitor, blocked the enzyme activity in the egg homogenate. In intact eggs, quinacrine blocked the CGR in a dose-dependent, egg-concentration-dependent manner. The inhibitory effect of quinacrine on the CGR could not be overcome by the phospholipase A2 activator mellittin or by the calcium ionophore A23187 [calcimycin]. Quinacrine did not inhibit sperm-egg binding or sperm incorporation. These results lend further support to the hypothesis that phospholipase A2 is involved in the CGR.


Accession: 005411647



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