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Abstract
The adsorption characteristics of a variety of synthetic peptide hormones and di-,
tri- and tetrapeptides on Cu(II) immobilized on two commercially available high-performance
chelating gels run under various experimental conditions are described. Methods for
determining the concentration of immobilized Cu(II) in situ are also described. The
Cu(II)-charged columns exhibit a net negative charge as judged from the significantly
higher retention of some basic peptides in the absence of NaCl in the equilibration
and elution buffers. At higher NaCl concentrations (2-4 M), aromatic interactions
seem to be superimposed on the metal ion affinity characteristics of the peptides.
The relationship between resolution of peptides and the concentration of immobilized
Cu(II) ions has also been established for the Chelating Superose gel where 40 mumol
Cu(II) ml-1 gel apparently gives the optimum resolution. The nature of the gel matrix
also plays a role in the resolution of some peptides, the extent of which is difficult
to predict. The results obtained also suggest that peptides containing aromatic and
hydroxy amino acids are retarded more than those which lack them. Moreover, these
same amino acids apparently strengthen the existing strong binding of peptides containing
His, Trp or Cys to a Chelating Superose-Cu(II) column. Dipeptides with C-terminal
His (i.e., X-His) are neither bound nor retarded on a column of Chelating Superose-Cu(II)
whereas those having the structure His-X are strongly bound. Some tri- and tetrapeptides
containing His were also found not to bind to the column. The underlying cause of
this anomalous adsorption behaviour is discussed and is ascribed to "metal ion transfer"
arising from the relatively higher affinity of such peptides towards immobilized Cu(II)
ions than the chelator groups (iminodiacetate) which are covalently bound to the gel
matrix.