A method of isolation and purification was developed for the major protein from the blood cells of the stolidobranch ascidian Pyura stolonifera. The protein, called ferreascidin because of its strong iron binding capacity (two Fe3+ per molecule), is the most aromatic protein that has been characterized, with 67% aromatic amino acids including 42% tyrosine and 17% 3,4-dihydroxyphenylalanine. It is a glycoprotein with an apparent sedimentation coefficient of 1.3 S determined by sucrose gradient centrifugation, corresponding to a molecular weight of 10 000 which is in agreement with that obtained from sedimentation equilibrium analysis (9800 ± 100). The presence of 3,4-dihydroxyphenylalanine, an amino acid involved in sclerotization of outer body tissues of invertebrates, supports the early proposition that the blood cells are involved in the formation of the test of the ascidian. Circular dichroism of whole cells indicated that the protein was isolated without major structural change.
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Dorsett et al. (1987) studied this question.