Characterization of the Defect in Heme Metabolism in Patients With Erythropoietic Protoporphyria

Abstract

The most pronounced biochemical characteristic in erythropoietic protoporphyria (EPP), an inherited disorder of heme biosynthesis, is the greatly increased protoporphyrin concentration in the red blood cell, which leads to photohemolysis when the cells are irradiated with visible light (9). Isoelectric focusing and protoporphyrin-hemoglobin binding experiments indicate that protoporphyrin is bound to hemoglobin at heme-binding sites (5). Experimental data of Schwartz et al. (10) were interpreted as indicating that the erythroid cell itself is the source of the protoporphyrin in the red blood cell. The increased protoporphyrin content can be explained by a decreased activity of heme synthetase or by an increased production of protoporphyrin in the heme metabolic pathway, both of which are indicated in the literature (7, 10). During systematic studies in the pathogenesis and the biochemical aspects of EPP, the activity of heme synthetase and the total porphyrin biosynthesis in blood cells of EPP patients were compared to the activities in normal blood cells.