Location and quantification of metal ions in enzymes combining polyacrylamide gel electrophoresis and particle-induced X-ray emission

A method is presented to identify and determine the relative amounts of protein-bound metal ions in situ. Proteins or their subunits are separated by SDS-PAGE, the appropriately dried gel sections are directly scanned by a collimated proton beam of 3 MeV energy, and the characteristic X-rays produced are detected. The determination of Fe content of an iron-sulfur protein (HiPiP), as well as the Fe and Ni analysis of the hydrogenase from Thiocapsa roseopersicina, have shown the feasibility of this technique