Analysis of developing enamel of the rat. I. Fractionation; protein and calcium content.

The developing or immature enamel of rat incisors contained 7.1% protein, 31.4% Ca2+, and about 1% carbohydrate. Sequential extractions with distilled water removed as much as 8.0% of the immature enamel which contained 58.5% of the whole enamel protein. The mean protein content of the water-extractable fractions was 51.9%; mean calcium content was 0.05%. About 22% of the water-extractable fraction was dialyzable; the dialysate contained 12.0% protein and the non-dialyzable fraction 41.0% protein. The residue that remained after the sequential extractions with water contained 3.6% protein and 32.7% Ca2+. Ninety-four percent of the residue was lost when demineralized by dialysis against 0.1 M EDTA at pH 7.0; included with the loss was 13.7% of the whole enamel protein. The nondialyzable, EDTA-water-soluble fraction contained 25.3% protein; the nondialyzable water-insoluble fraction contained 50.4% protein. The latter fraction accounted for about 25% of the whole immature enamel protein.