Über Aminoendgruppen von Kollagen, III. Acetylierte Aminoendgruppen in den Untereinheiten der Peptidketten des Kollagens

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Abstract
0.1 mol. of free a-amino groups per 1000 mol. of amino acid residues was determined in acid-soluble and in insoluble collagen by dinitro-phenylation. This corresponds to only one tenth of that expected if one amino end group occurred in each of the three peptide chains of collagen. The [epsilon]-amino groups of collagen could be completely sub-stitutedby l-fluoro-2,4-dinitrobenzene, if the reaction was carried out in the presence of a denaturing agent (2.5 M NaClO4). In the absence of such a compound, the [epsilon] -amino groups are only incompletely dinitrophenylated. Acetyl groups were demonstrated in acid-soluble collagen. Some of these (6 mol/1000 mol. amino acids) could not be removed from the protein by hydroxylamine and are therefore N-acetyl residues. The latter can only be attached to [alpha] -amino groups, since all [epsilon] -amino groups are in the free form. The acetyl residues were determined in the form of dinitrophenyl-acethydrazide after hydrazinoly-sis of the protein. The presence of N[alpha] -acetyl residues in the above quantities is interpreted as showing that the peptide chains of collagen consist of an average of six subunits, whose amino end groups are acetylated.