Amino acid composition of aragonitic concholin in the shell of Arctica islandica

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Abstract
The distribution of amino acids within the two aragonitic shell layers of modern specimens of the mollusc Arctica islandica (Linne) has been studied in detail. The mean total hydrolyzed amino acid content was 19 nmol/mg in the inner layer and 15 nmol/mg in the outer layer. No significant difference in amino acid composition could be found between the two layers. The layers contained minor amounts of free amino acids which made up 0.3-0.7% of the total hydrolyzed amino acid content. The composition of the free amino acid fraction was very similar in each of the two layers, but differed somewhat from the total hydrolyzed fraction. The total hydrolyzed fraction was dominated by aspartic acid, glycine, alanine and glutamic acid, which together made up 62% of the total amount of amino acids, whereas the free fraction was dominated by Asp, Ser, Gly and Tyr. Amino acid content and composition within a single layer showed little variation from umbo to the ventral margin. The amino acid composition is in accordance with previously reported data on similar mineral structures which support the theory of structure specific rather than species specific amino acid composition.