Erythropoietic protoporphyria and lead intoxication: the molecular basis for difference in cutaneous photosensitivity. II. Different binding of erythrocyte protoporphyrin to hemoglobin.

Abstract

A B S T R A C T Acidic solvenits extract the same porphyrin-protoporphyrin-from the erythrocytes of patients with either erythropoietic protoporphvria or lead intoxication. However, extractable protoporplhyrin disappears rapidly, both in vivo alnd in vitro, frolmi ervthrocytes in erythropoietic protoporphyria but slowly, if at all, in lead intoxicationi. Consistent w-ith these observations, fluorescence spectroscopy revealed that the intracellular state of the erythrocyte protoporphyrin is different in the two diseases. Spectrofluorometric measurements coupled with fractionations and biochemical syntheses showed that in erythropoietic protoporphyria the protoporphyrin is bound as the free base to lhellmoglobin molecules at sites other than the heme bilnding sites. In lead intoxication the fluorescent porphyrin is also bound to hemoglobin but is present as zinlc protoporphyrin. The data suggest that the zilnc protoporphyrin is bound at heme binding sites. Acidic extraction solvents remove the chelated zinc, but zinlc protoporphiyrinl may be extracted intact from erythrocytes w-ith acetone, ethaniol, or the detergent Ammnonyx-LO.

The molecular defect of ferrochelatase in a patient with erythropoietic protoporphyria.

“…The patient was a 12-yr-old white girl, with the cutaneous photosensitivity characteristic of EPP. Protoporphyrin concentrations in her erythrocytes, plasma, and stool were markedly elevated (Table 1), and erythrocyte porphyrins consisted almost exclusively of free, not Zn-chelated, protoporphyrin (13). Ferrochelatase activity, as determined by an assay based on the ability of lymphocytes to form protoporphyrin from its precursor, 6-aminolevulinic acid (6), indicated that the proband's enzyme activity was about one-half (46.5%) the normal level (Table 1).…”

Diagnosis, Evaluation, and Treatment of Lead Poisoning in General Population

“…Ferrochelatase is responsible for the incorporation of iron into protoporphyrin IX to form heme. As a result of inhibition, protoporphyrin accumulates in erythrocytes, with the majority binding to zinc and to form zinc protoporphyrin [6]. Table 3 shows the various symptoms associated with lead poisoning in the two groups.…”

Indices of potential lead hazard.

“…This is also the case in iron deficiency anemia (133). In both lead absorption and iron deficiency, it is the Zn chelate of protoporphyrin that accumulates (133,134) while in EPP it is mainly the free, basic form of protoporphyrin (134). The Zn chelate is bound to the heme site on hemoglobin, while the basic form is bound to nonheme sites (134).…”

“…In both lead absorption and iron deficiency, it is the Zn chelate of protoporphyrin that accumulates (133,134) while in EPP it is mainly the free, basic form of protoporphyrin (134). The Zn chelate is bound to the heme site on hemoglobin, while the basic form is bound to nonheme sites (134). Acidic organic solvents are used to extract "free" erythrocyte prophyrins (free of the Zn), while the intact Zn chelate can be extracted with acetone, ethanol or the detergent Ammonyx-LO (134).…”