Characterization of protoporphyrin in red blood cells of patients with erythropoietic protoporphyria.

It was investigated whether the protoporphyrin that can be extracted from red blood cells of erythropoietic protoporphyria (E.P.P.) patients is present in the cells as free molecules or protein-bound. With isoelectric focusing and with starch gel electrophoresis it could be shown that virtually all protoporphyrin in the erythrocytes is protein-bound. It is very likely that the protoporphyrin is bound to hemoglobin at heme-binding sites. This was indicated by several observations: 1. With isoelectric focusing the protoporphyrin-protein complex is focused at a pH only slightly higher than the isoelectric point of hemoglobin. 2. With chromatography on Sephadex columns it appeared that hemoglobin and the protopotphyrin-protein complex have the same molecular weight. 3. A Heme-protoporphyrin exchange occurred when the heme-globin bond was labialized by conversion to hemiglobin. The resulting protoporphyrin-hemoglobin complex had the same electrophoretic mobility with starch gel electrophoresis as the protoporphyrin-protein complex, extracted from red blood cells of E.P.P. patients.