Sperm head decondensation by a high molecular weight fraction of sea urchin egg homogenate

Sperm nucleus decondensing activity (NDA) of eggs has been investigated using the gametes of the sea urchin, Lytechinus variegatus. To assay for NDA, isolated sperm heads were exposed to homogenate from mature unfertilized ova and then examined with phase-contrast optics. NDA is retained by dialysis and requires Ca++ at the time of homogenization as well as at the time of assay. Other divalent cations (Mg++, Sr++, Ba++, Mn++) can substitute for Ca++ but are much less effective. NDA is stable to cold (-20 degrees C, -76 degrees C) but not to heat (56 degrees C). The pH activity optimum is in the range 7-9. NDA is present in the supernatant after centrifugation at 150,000 g for 105 minutes. It elutes shortly following the void volume on a Sephacryl S-200 column, with an approximate M.W. of 100,000 daltons.