When calfskin collagen is treated with trichloroacetic acid at 90 degrees C, it is hydrolyzed to a mixture of peptides, some of which are quite small. Cleavage of collagen by acid seems to occur at bonds between proline (or hydroxyproline) and other amino acids, with only a limited specificity for which amino acid donates its amino group to the susceptible peptide bond.
Amino Acids Animals