Zinc Protoporphyrin Formation When iron levels are low, the body’s attempt to continue hemoglobin production leads to an interesting substitution: - The enzyme ferrochelatase, which normally inserts iron into protoporphyrin IX to form heme, instead incorporates zinc. - This results in the formation of zinc protoporphyrin (ZPP) instead of heme. The presence of increased ZPP has several important implications: - ZPP cannot function as hemoglobin, as it lacks the oxygen-carrying capacity of iron-ba