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The Importance of Heme Metabolism

Quiz
 
Here are some examples of hemoproteins. Notice that they all are involved in some way with oxygen or with oxidation processes.

Hemoproteins are synthesized in all mammalian cells. Here are the major sites.

Examples of Hemoproteins
These are only a few of the many hemoproteins. Also given is information about their turnover to emphasize the need for resynthesis of the protein and the heme.

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.
Major Sites of Hemoprotein Synthesis

Erythropoietic tissue

  • polychromatophilic erythroblasts
  • reticulocytes
  • normoblasts (nucleated erythrocytes in bone marrow)

Liver

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