The “nondialyzable” fraction obtained from ichthyocol digested with collagenase

Abstract Kinetic analysis was made of the dialysis of digests of ichthyocol gelatin prepared with collagenase. It was found that most, if not all, of the peptides in such digests are dialyzable, but at greatly different rates. First, there is a class of slowly dialyzable peptides that contain most of the tyrosine, ester groups, and carbohydrate moieties of the parent protein molecule. Second, there is a class of slowly dialyzable peptides, which are rich in the polar amino acids and appear to originate from the polar or “noncrystalline” regions of the protein molecule. Third, there is a class of rapidly dialyzable peptides that are rich in proline and hydroxyproline and appear to originate from the “crystalline” regions of the collagen molecule. After 48 hr., the most slowly dialyzable peptides remain in an aggregate fraction which, operationally, has been designated a “non‐dialyzable” fraction. It has been established that the aggregate peptides have, relative to original gelatin, increased contents of glutamic acid, aspartic acid, and lysine, and contain major portions of the carbohydrate, tyrosine, and hydroxylamine‐sensitive (“ester‐like”) bonds of gelatin. However, they have relatively decreased contents of proline, hydroxyproline, arginine, and leucine. Their Contents of glycine and alanine are relatively unchanged. Dinitrophenylation studies indicated that the average peptide length of the “nondialyzable” peptides was 11–15 residues. On the basis of these and other studies, a representation is made of the polar and nonpolar regions of the collagen molecule.