Zinc protoporphyrin

Zinc protoporphyrin (ZPP) is a compound found in red blood cells that is typically elevated in conditions where the production of heme, a component of hemoglobin, is disrupted. This can occur in a variety of medical conditions, including lead poisoning, iron deficiency anemia, and certain genetic disorders such as sideroblastic anemia and thalassemia.

Structure and Function

Zinc protoporphyrin is a porphyrin molecule with a zinc ion coordinated in the center. It is formed when zinc, instead of iron, is incorporated into the protoporphyrin IX ring during heme synthesis. This typically occurs when there is a deficiency of iron, or when the enzyme ferrochelatase, which normally inserts iron into protoporphyrin IX, is inhibited.

Zinc protoporphyrin has no known biological function. Unlike heme, it cannot bind oxygen and therefore cannot participate in oxygen transport or storage in the body. However, its presence can serve as a useful marker for disruptions in heme synthesis.

Clinical Significance

Measurement of zinc protoporphyrin levels in red blood cells is a common diagnostic test for lead poisoning. Lead inhibits the enzyme ferrochelatase, leading to an accumulation of protoporphyrin IX, which then binds zinc to form ZPP. Elevated levels of ZPP can therefore indicate lead exposure.

Zinc protoporphyrin levels can also be elevated in conditions of iron deficiency. Without sufficient iron, the body may incorporate zinc into protoporphyrin IX instead, leading to increased ZPP. This can occur in iron deficiency anemia, as well as in conditions where iron is present but cannot be utilized properly, such as in sideroblastic anemia.

In addition, certain genetic disorders that affect heme synthesis can lead to elevated ZPP levels. These include various forms of thalassemia and porphyria.

See Also

• Lead poisoning
• Iron deficiency anemia
• Sideroblastic anemia
• Thalassemia
• Porphyria
• Heme
• Hemoglobin
• Red blood cells