ASSEMBLY OF THE SEA-URCHIN EXTRAEMBRYONIC HYALINE LAYER - CA2+ AND MG2+ ACT INDEPENDENTLY AND AT DIFFERENT SITES ON THE PATHWAY LEADING TO HYALIN-GEL FORMATION

We have studied the interactions of Ca2+ with the sea urchin extraembryonic coat protein hyalin. As reported previously, Ca2+ alone was ineffective in inducing hyalin-gel (large aggregate) formation. This reaction required the additional presence of Mg2+ and NaCl. However, the results of tryptic digestion and nondenaturing agarose gel electrophoresis experiments demonstrated that Ca2+ could induce hyalin self-association into small aggregates in the absence of Mg2+ and NaCl. Magnesium did not modulate the interactions of Ca2+ with hyalin. In addition, Mg2+ had minimal effects on the conformation of hyalin. These results have been incorporated into a model delineating the pathway leading to hyalin-gel formation. © 1991.