Fertilization acid of sea urchin eggs is not a consequence of cortical granule exocytosis.

Sea urchin eggs treated with 10 mM NHC1 release a "fertilization acid" although cortical granule exocytosis does not take place. If the eggs are inseminated following ammonia activation, the cortical reaction occurs and a fertilization membrane elevates in the absence of detectable acid release. Examination by electron microscopy of eggs fixed between ammonia activation and insemination confirms the presence of intact granules. Thus, the fertilization acid is not caused by the release of the cortical granules. Ammonia treatment of fertilized eggs stimulates further release of acid. The release of acid can occur repeatedly in ammonia activated eggs if they are washed into normal seawater between successive ammonia treatments. Our results suggest that the release of fertilization acid is related to some metabolic process which can be turned "on or off".