The Nature of the Chelate Structures Formed by Copper(II) and Ovalbumin in the Biuret Reaction

Abstract

A spectrophotometric study was made of the interaction, in alkaline solution, of copper(II) with ovalbumin and several ligands of low molecular weight at several different atomic ratios of nitrogen/copper. The results indicate that the absorbance and chemical reactivity of the ovalbumin-copper(II) complex cannot be attributed to the presence of one particular chelate structure. It is suggested that the ovalbumin-copper(II) complex is a heterogeneous mixture of chelate structures in which the copper(II) is bonded to oxygen (in the enolate form) and nitrogen atoms in the several different combinations possible within the same polypeptide chain. It is also suggested that the actual arrangement of bonds in any one chelate structure is probably determined by both the nature of the amino acid residues and the configuration of the ovalbumin molecule in the immediate vicinity.