THE RATIO OF ERYTHROCYTE ZINC-PROTOPORPHYRIN TO PROTOPORPHYRIN-IX IN DISEASE AND ITS SIGNIFICANCE IN THE MECHANISM OF LEAD TOXICITY ON HEME-SYNTHESIS

Protoporphyrin and zinc-protoporphyrin were measured in the erythrocyt es of normal subjects, workers exposed to lead and patients with iron deficiency and erythropoietic protoporphyria (EPP). Results showed sig nificantly higher levels of zinc-protoporphyrin in the lead-exposed wo rkers (P<0.0001), patients with iron deficiency (P<0.0001) and EPP pat ients (P<0.001) compared with normal subjects. The lead-exposed worker s showed the highest levels of zinc-protoporphyrin, which were signifi cantly greater than both the iron-deficient and EPP patients (P<0.0001 ). They also showed a higher ratio of zinc-protoporphyrin to free prot oporphyrin compared with normal subjects (P<0.0001) but no significant difference in this ratio was found when compared with iron-deficient patients (P=0.1). These results are discussed in light of the controve rsy concerning the mechanism of formation of zinc-protoporphyrin in le nd exposure.