Chemical nature of proteins in the placoid scale of the blue shark, Prionace glauca L

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Abstract

Powdered placoid scale was fractionated with differential density-flotation into three fractions, Frs L (density, 1.7 to 2.3), M (more than 2.3 to 2.6) and H (more than 2.6), in a proportion of 11:2:1. Fr L was regarded as dentine and Fr H as enameloid. Protein content of dentine was 16.7 per cent and of enameloid 5.6 per cent. Collagen was the major protein in both. After demineralization with 0.5 M EDTA, collagen was extracted with 0.5 M acetic acid at 75 °C. Proteins that were soluble in 0.5 M EDTA and in 10 mM NaOH after the extraction of collagen, A, were fractionated into four groups of proteins, and three were phosphoproteins of varying phosphate contents (about 4, 8 and 40 moles per 100 amino acids). Other noncollagenous proteins of low phosphate contents (2 moles) were divided by solubility differences into 6 M-guanidine-soluble (B), thiol-guanidine-soluble (C) and thiol-guanidine-insoluble proteins (D). The proportion of collagen: A: B: C: D was 66:15:3:4:12 in dentine and 44:19:4:3:30 in enameloid. The amounts of protein groups in A also differed notably in the two. The chemical compositions of phosphoproteins in A resembled those reported for phosphoproteins of mammalian dentine. Compositional patterns of B, C and D were similar to the gross amino acid composition of mature mammalian enamel and close to those reported for peptides released from the amino-terminal region (B and D) and carboxy-terminal region (C) of procollagen.

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    Present address: Department of Oral Microbiology, Matsumoto Dental College, Shiojiri, 399-07 Japan.

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