Formation and spectral properties of copper (II) ion complexes of the NH2-terminal pentapeptide from sperm whale myoglobin and of certain tetra- and pentapeptides.

1. The association and ionization constants of copper(I1) complexes of glycylglycylglycylglycine, L-alanylglycylglycylglycine, glycylglycylglycylglycylglycine, L-alanylglycylglycylglycylglycine, glycylglycylglycylglycyl-L-alanine, L-valyl-Lleucyl-L-seryl-L-glutamylglycine, and L-valyl-L-leucyl-Lseryl-L-glutaminylglycine were computed from potentiometric measurements. The acid ionization constants of the free peptides were determined. 2. The visible absorption spectra of the reaction mixtures were resolved to show that identical species of the peptide complexes gave identical wave lengths of maximum absorbance with some variation in the molar extinction values. 3. Cotton effects were observed in the visible range for peptide complexes containing optically active amino acid residues. In each case the circular dichroism spectrum showed a single negative band or perhaps closely overlapping negative bands. The general form of the spectra was similar to that observed with tripeptide complexes containing L-alanyl residues, and indications of an additivity effect in substitutions in the chelate rings are presented. In all cases optically active transitions were observed near 300 mp. 4. The contribution of the NH,-terminal L-alanyl moiety in complexes of peptides containing 2,3, or 4 more subsequent glycyl residues was constant as to optical rotatory power, in the visible range, although the tribeptide complex differed in wave length of the extremum from the tetraand pentapeptide complexes. 5. The optical rotatory properties of the fully formed