Date of Award

Spring 1996

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

N Dennis Chasteen

Abstract

Shell deposition within the bivalve mollusc Mytilus edulis is regulated by the macromolecules of the extrapallial fluid (EP fluid). These mineralization regulating macromolecules are thought to be responsible for the nucleation, growth regulation and growth cessation of the CaCO$\sb3$ mineral crystals that will inevitable constitute $\geq$95% of the mature shell.

This dissertation presents the results of the purification and characterization of the major EP fluid protein of the bivalve Mytilus edulis. The major EP fluid protein was determined to comprise 56% of the total fluid protein and to consist of 7.25% by weight carbohydrate. The protein was purified though a series of chromatographic procedures and, once pure, was shown to have a molecular weight of 28,300 amu and an isoelectric point of 4.85.

N-Terminal amino acid sequence analysis showed the primary protein structure to be, Asn-Pro-Asp-Asp-X-X-Asp-Asp-X-X-Asp-Ala-Pro-Ile-Val-Glu-X-X-Asp- (where X = an unknown amino acid residue). This amino acid sequence shows a repeat sequence similar to the theorized - (Asp-X) - (X = Gly) shell organic matrix repeat sequence proposed to act as a template for CaCO$\sb3$ crystal growth. Additionally, the EP fluid protein shows similarities with mollusc shell soluble organic matrix proteins in its amino acid composition with glutamic and aspartic acid residues being the two most abundant amino acid residues.

Lastly, the EP fluid protein was shown to bind calcium and in so doing self-assemble into higher order protomers. Protomers composed of as many as 32 subunits were identified. The ability to self-assembly is one of the most intriguing properties ascribed to organic matrix of molluscan shells. The results of this dissertation suggest that the major extrapallial fluid protein may be a building block of the organic matrix of the shell. The proposed model of the EP fluid protein protomer formation may give insight into how matrix assemble takes place.

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