A partially purified phosphopeptide fraction with low N/P ratio has been obtained from the small intestinal contents of rats, which was collected at the first one hour after 1.5 hr spaced-feeding of the diet containing 20% casein. After precipitation of protein with trichloroacetic acid, acid-soluble fraction was chromatographed on the column of Sephadex G-25. A fraction containing large peptide(s) having the N/P atomic ratio of about 7 to 9 and free from lower molecular substances was rechromatographed with Sephadex G-50. This fraction, amounted nearly 30% of the total non-protein nitrogen of the intestinal contents, showed high calcium-binding activity as determined with Chelex-100. These results suggest a special role of phosphopeptide stage on the stimulating calcium absorption in the intestinal tract during the digestion of casein.
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Naito et al. (1972) studied this question.