The folded protein complexes of interest separate cleanly and predictably without the risk of denaturation due to the specific properties of the polyacrylamide gel, electrophoresis buffer solution, electrophoretic equipment and standardized parameters used. The separated proteins are continuously eluted into a physiological eluent and transported to a fraction collector. In four to five PAGE fractions each the different metal cofactors can be identified and absolutely quantified by high-resolution ICP-MS. The associated structures of the isolated metalloproteins in these fractions can be specifically determined by solution NMR spectroscopy.