“…The method of Sanger (1945) modified by Courts (1954a) for gelatin has been used as a valuable tool for following the modifications in the chain length and in the types of peptide bonds cleaved during the transformation of collagen (Courts, 1954a(Courts, , 1954b(Courts, , 1955(Courts, , 1959(Courts, , 1960(Courts, , 1961(Courts, , 1980. The principle of the method is the addition of 2, 4-dinitrofluorobenzene (DNFB) to free amino groups to give the dinitrophenyl derivatives (DNP), which are sufficiently stable during subsequent hydrolysis of the protein.…”