Zinc Protoporphyrin (ZPP)

Zinc protoporphyrin (ZPP) is a compound found in red blood cells when heme production is inhibited by lead and/or by lack of iron.  Instead of incorporating a ferrous ion, to form heme, protoporphyrin IX, the immediate precursor of heme, incorporates a zinc ion, forming ZPP. The reaction to insert a ferrous ion into protoporphyrin IX is catalyzed by the enzyme ferrochelatase. It was already known at this time that non-heme Protoporphyrin IX levels were elevated in these conditions, but prior investigators had used extraction methods that converted ZPP to unbound Protoporphyrin IX. The early literature is sometimes confusing, and results are hard to compare without detailed examination of the measurement methods and the conversion factors used to report the results. Reports may refer to Free Erythrocyte Protoporphyrin (FEP) or Erythrocyte Protoporphyrin (EP or EPP).