Degradation of yolk proteins in sea urchin eggs and embryos

Yolk granules isolated from unfertilized and fertilized eggs of the sea urchins, Hemicentrotus pulcherrimus and Anthocidaris crassispina, were incubated in acidic media, and the protein components were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By the incubation, a protein (molecular weight 180,000 in H. pulcherrimus and 178,000 in A. crassispina) most abundant in unfertilized eggs decreased, while proteins (molecular weight 61,000, 72,000, 94,000, 114,000 in H. pulcherrimus and 56,000, 70,000, 92,000, 112,000 in A. crassispina) dominant in developed embryos increased. Neither alkaline nor neutral condition resulted in such changes in the electrophoretic patterns of proteins as observed in acidic media. Experiments with various inhibitors of proteases suggested that thiol protease(s), such as cathepsin B, may be the most important enzyme(s) in the degradation of yolk proteins in embryogenesis of the sea urchin.