Studies of serum protein complexes with nickel using crossed immunoelectrophoresis

Crossed immunoelectrophoresis of human serum spiked with nickel in the range 0.85-24 mmol Ni/L was used to study nickel-protein complexes. These high concentrations, which are far higher than the physiological level (approximately 7.8 nmol/L), were used to saturate both high and low affinity binding sites. Addition of increasing amounts of nickel resulted in dose-dependent changes of the electrophoretic patterns of prealbumin, alpha-1-lipoprotein, alpha-1-antitrypsin and alpha-2-macroglobulin. Radioactive 63Ni was used for crossed immunoelectrophoresis autoradiography experiments for further identification of nickel-protein complexes. When a 63Ni pulse of 740 kBq/application was used, many human serum proteins were labeled. When using a 63Ni pulse of 185 kBq/application only albumin and alpha-1-antitrypsin were visualized clearly. The binding of large amounts of nickel to albumin, visualized by autoradiography, may reflect the high abundance of albumin in human serum as compared to other serum proteins. Addition of nickel to serum proteins resulted in liquid phase precipitation of serum proteins, and rocket immunoelectrophoresis was used to demonstrate that IgG in particular is precipitated. This precipitation of serum proteins may disturb the elution profile when chromatographic techniques are used to analyze nickel-protein complexes. Consequently, immunoelectrophoretic methods may also be attractive alternatives to column chromatographic techniques. The present study demonstrated that, besides the nickel-binding of albumin and alpha-2-macroglobulin, several other serum proteins have nickel-binding affinity.