Biphasic activation of Fyn kinase upon fertilization of the sea urchin egg.

Fertilization results in the tyrosine phosphorylation of several egg proteins within minutes of sperm-egg binding and inhibitor studies have shown that tyrosine kinase activity is required for many aspects of egg activation. The present study demonstrates the presence of p59c-fyn kinase in the sea urchin egg and examines the effect of fertilization on the activity of this enzyme. Fertilization had little effect on Fyn kinase activity during the first 2 min after insemination; however, activity had increased approximately eightfold between 5 and 15 min postinsemination. This initial, rapid increase in kinase activity was followed by a period of slightly elevated kinase activity, which was two- to threefold higher than that in the unfertilized egg. Bindin, as well as various parthenogenic agents known to activate the calcium- and pH-mediated pathways of egg activation, failed to elicit any change in enzyme activity, indicating that activation of the kinase required sperm-induced egg activation. However, phorbol ester treatment did induce a slow increase in kinase activity within 30 to 60 min of administration. These findings indicate that the p59fyn kinase is activated within minutes of fertilization and may play a role in the egg activation process.