The Importance of Heme Metabolism
Hemoproteins are synthesized in all mammalian cells. Here are the major sites.
Hemoglobin is the quantitatively most important hemoprotein.
- It is the carrier of oxygen in the blood.
- The body contains 750 grams (1.6 pounds) of hemoglobin; it is replaced every 120 days.
- Normal hemoglobin turnover requires synthesizing 6-8 grams of new hemoglobin daily, a process which uses about 14% of the dietary amino acids. 300 milligrams of heme are synthesized daily for conjugation with the newly synthesized globin protein.
Cytochromes are present in the mitochondria and in the endoplasmic reticulum.
- They participate in important electron transfer reactions.
- Their half life is about 132 hours.
Catalase and peroxidase react with hydrogen peroxide.
- These enzymes protect the body against uncontrolled oxidation by hydrogen peroxide.
- Their half life is about 20 hours.
Tryptophan oxygenase is a hemoprotein of intermediary metabolism.
- It catalyzes the conversion of tryptophan to N-formylkynurenine, using oxygen as the oxidant.
- Its half life is only about two hours.
Erythropoietic tissue
- polychromatophilic erythroblasts
- reticulocytes
- normoblasts (nucleated erythrocytes in bone marrow)
Liver