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of the incisor teeth, and indicate that maturation of enamel is accompanied by a loss of protein components rich in proline and histidine and poor in serine.3. Small amounts of both 3-and 4-hydroxyproline were detected in all protein fractions. The 3-hydroxyproline: 4-hydroxyproline ratio in enamel was higher than that of either bovine dentinal or cemental collagen, suggesting that at least a portion of the hydroxyprolines are true constituents of the organic matrix of developing enamel.

1. The organic matrix of enamel from erupted bovine teeth has been found to be composed mostly of small peptides containing principally aspartic acid, glycine, glutamic acid and serine. 2. A small amount of higher-molecular-weight components has been isolated by various procedures. One non-diffusible fraction was found to be heterogeneous in the ultracentrifuge, and composed principally of material that by gel filtration indicated a molecular weight greater than 30000. These components were largely carbohydrate in nature (glycoproteins and glycopeptides), containing only small amounts of amino acids.

The proteins, soluble and insoluble at neutral pH, of relatively mature enamel of two different species of sharks were distinctly different from both collagen and embryonic enamel proteins and similar to the proteins isolated from mature human and bovine enamel.

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