The overall objective of this study is to characterize the components of the cell surface of the sea urchin egg and to elucidate the role of these components in the initial events in fertilization. 1) We will continue studies on the components of a cell surface complex isolated from eggs that consists of the plasma membrane, coated on the outer side with peripheral proteins of the vitelline layer and on the inner side with cortical vesicles. Following further subfractionation the vitelline components, plasma membrane, cortical vesicle membrane, and the contents of the cortical vesicles will be isolated, and analyzed comparatively for polypeptides, lipids, and marker enzymes. To obtain a clearer picture of the fate of these components following fertilization, they will be compared with known components of the hyaline layer and the fertilization envelope. 2) The ion permeability of vesicles prepared from the plasma membrane, the cortical vesicle membrane and a mosaic membrane consisting of both of them will be measured to determine if one of these membranes is responsible for the enhanced influx of Ca++ and Na+ into the egg observed upon fertilization. 3) We will investigate the possibility that Ca++ dependent breakdown and arachidonic acid release. The cell surface complex may be an excellent model to study the kinetic and functional relationships between secretion and arachidonic acid production and metabolism. 4) The structure of the sulfated polysaccharides in egg jelly coat will be studied to define the structural differences that result in species specific induction of the acrosomal reaction in sperm. Using jelly coat as an affinity ligand we will undertake the isolation of the protein on the surface of the sperm that functions as a receptor of jelly coat. The properties and mode of action of the isolated receptor in inducing the acrosomal reaction will be studied. 5) Using binding, or antibody prepared towards a glycopeptide fragment of the receptor as tools, we will isolate the receptor for sperm from solubilized egg cell surface membranes. The purified receptor will be characterized and the structural components of it responsible for both sperm adhesion and species specificity will be defined.