Speciation of metal ions in proteins by combining PIXE and thin layer electrophoresis

Particle induced X-ray emission (PIXE) spectroscopy is a simple and conveni ent method of quantitative multielemental analysis with sensitivities in th e mu g/g range, that can be successfully used for trace analysis of metal i ons in proteins or enzymes. However, due to its elemental character the tec hnique alone is not a priori suitable for speciation. Keeping track of the metal ions of interest throughout a proper biochemical separation technique , on the other hand, could be a useful strategy for speciation. Different v ersions of thin layer electrophoresis (polyacrylamide gel, agarose or cellu lose acetate electrophoresis) are very effective and sensitive methods to s eparate proteins or protein fragments. Due to the high absolute sensitivity of PIXE the metal ions concentrated in the narrow bands of an electrophero gram can be in situ successfully detected. The present paper describes this unique combination of biochemical separation and ion beam analysis which s ignificantly extends the information obtained from electrophoresis. Illustr ative applications are given and the advantages and limitations of the meth od are discussed. Possible extensions of the technique are also outlined.