Characterization of water in unfertilized and fertilized sea urchin eggs

The water in unfertilized and fertilized sea urchin eggs was characterized with a proton nuclear magnetic resonance (NMR) titration method assuming fast proton diffusion (FPD) between water compartments. This method involves stepwise dehydration with sequential T₁ relaxation time and water content determinations. The results analyzed by the FPD model give evidence of intracellular water compartments with three different correlation times: 6 × 10⁻¹² sec (bulk water), 1 × 10⁻¹⁰ sec (structured water) and about 2 × 10⁻⁹ sec (bound water). Fertilization is accompanied by a substantial increase in bulk water (from 111 to 414 g H₂O per 100 g dry mass) and by a decrease in the water of hydration (from 128 g to 56 g per 100 g dry mass). This study shows that 54% of the water in the unfertilized sea urchin egg has motional properties different from bulk water and that this percentage decreases dramatically shortly after fertilization. Most of the change in T₁ relaxation rate observed at fertilization can be accounted for by uptake of bulk water associated with elevation of the fertilization membrane.