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Erythroid ferrochelatase activity has been studied in the normoblasts of patients with porphyria variegata and protoporphyria. Two methods were used for the investigation: one using intact cells and the other lysed cells, each measuring the amount of haem synthesized by normoblasts. In patients with porphyria variegata, ferrochelatase activity estimated by both methods was approximately 50% of the normal, and in protoporphyria the ferrochelatase activity was normal in intact normoblasts but was 20% of the normal in sonicated normoblasts (marrow lysates). It is suggested therefore that in porphyria variegata a dominantly inherited structural gene mutation results in an active ferrochelatase whereas in protoporphyria the genetic mutation results in an unstable ferrochelatase. The mechanism of the enzyme instability is not known though a number of postulates are discussed.

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