Results are reported of a potentiometric and spectrophotometric study of the H + and Cu2+ complexes of the tetra peptides X-Gly-Gly-G ly, G ly-X-G ly-Gly, G ly-Gly-X-G ly, and Gly-Gly-G ly-X where X is the proline (Pro) and sarcosine (Sar) residue (Gly = glycine). All the tetrapeptides (HL) form the series of complexesand [CuH-,L] (charges omitted). The ligands Gly-X-Gly-Gly also form the bis-complex, [CuL,]. When inserted in a peptide chain the Pro and Sar residues cannot co-ordinate t o Cu2+ through their peptide nitrogens since they d o not possess ionizable protons. In addition the Pro residue tends t o force the peptide chain to form a 'pturn' and so adopt a 'bent' conformation. These studies demonstrate the formation of a large chelate ring when tetrapeptides containing Pro (and, to a smaller extent, Sar) in the second or third positions co-ordinate t o Cu2+. This ring spans the terminal residues of the peptide chain and locks the peptide into a 'bent' or 'horse-shoe' shaped conformation. Cu2+ could therefore play an important role in activating oligopeptides (e.g. neuropeptides) containing proline.

Mittels potentiometrischer und spektrophotometrischer Messungen werden die Protonierungs‐ und Cu(II)‐Komplexbildungskonstanten der Tetrapeptide (I)‐(IV) untersucht.

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