| Summary: | Thesis (Ph.D.)--Memorial University of Newfoundland, 2007. Biochemistry Includes bibliographical references (leaves 158-177) The yolk granule is the most abundant membrane-bound organelle present in sea urchin eggs and embryos. The major protein component of this organelle, major yolk protein/toposome, accounts for approximately 50% of the total yolk protein and has also been shown to be localized to the embryonic cell surface. Biochemical and cell biological analysis in several laboratories have defined a role for toposome in mediating membrane-membrane interactions. -- In this study we have examined calcium-toposome interaction. Increasing concentrations of calcium resulted in an increase in alpha helical content from 3.0 to 22.0%, which occurred with an apparent dissociation constant (calcium) of 25 μM. In parallel experiments, toposome binding to liposomes required similar concentrations of calcium; an apparent dissociation constant (calcium) of 25 μM was recorded. Endogenous tryptophan fluorescence measurements, both in the presence and absence of liposomes, demonstrated that toposome tertiary structure
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