Metal complexation by the peptide-bound maillard reaction products N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine.

Although the Maillard reaction between proteins and carbohydrates is of central importance for food processing and in vivo processes, only little is known about changes of the metal-binding properties induced by protein glycation. The purpose of this study was to examine the complex formation of the quantitatively important peptide-bound Maillard reaction products (MRPs) N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine with the biologically relevant metal ions copper(II) and zinc(II). The MRPs were synthesized as the N(alpha)-hippuryllysine derivatives in order to block the coordination function of the alpha-amino group. Stability constant measurements were performed in aqueous solution using pH potentiometry. N(alpha)-Hippuryl-N(epsilon)-fructoselysine forms moderate Cu(II) complexes (Log(10) K(1) = 5.8; Log(10) K(2) = 4.0) but fails to form any complexes with Zn(II). N(alpha)-Hippuryl-N(epsilon)-carboxymethyllysine gives slightly stronger complexes with Cu(II) (Log(10) K(1) = 7.3; Log(10) K(2) = 6.3), but again no complexation with Zn(II) was observed. These results show that post-translational modification of proteins by carbohydrates leads to the formation of new coordination centers for metal ions within a protein chain. Further studies are necessary to clarify the consequences of this phenomenon in terms of protein quality and physiological processes.