Yields of tubulin paracrystals, vinblastine-crystals, induced in unfertilized and fertilized sea urchin eggs in the presence of D2O.

The effect of D2O on the crystallization of polymerizable tubulin in sea urchin egg cytoplasm was investigated by estimating the yield of "vinblastine (VB)-crystals" by directly measuring the dimensions of the crystals produced and by protein assays of the crystal isolates. The yield of VB-crystals in mature unfertilized eggs was fairly constant; it neither increased nor decreased in the presence of D2O. On fertilization, the yield of crystals decreased markedly as compared with yields from unfertilized eggs; but, the yield was restored to the value for unfertilized eggs when an adequate concentration of D2O was present during incubation. These results are evidence that tubulin molecules in unfertilized sea urchin eggs are in the polymerizable state but become masked and partly unpolymerizable after fertilization and the D2O releases the masked state and converts unpolymerizable tubulin molecules into active and polymerizable state.