“…Ammonium sulfate fractionation, ion-exchange chromatography, and gel filtration led only to partial separation. Acetone fractionation, which is used in the procedure of Straub (1940) to separate hemoglobin from isoenzyme 1, led to complete inactivation of isoenzyme X. With preparative electrophoresis of partially purified material containing isoenzymes X, 3, and heme protein, the isolation of isoenzyme X was finally possible.…”