Heme and Iron

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Two Steps of Heme Degradation
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Quiz
 
Heme is degraded in two steps to bilirubin, which is conjugated to glucuronic acid and excreted

The first reaction is cleavage of the heme ring by a microsomal heme oxygenase.

The substrates for the reaction are

  • heme
  • three molecules of oxygen
  • NADPH

The is a cleavage of the ring between the I and II pyrrole rings.

  • The alpha-methylene group is released.
  • The product is symmetric with respect to the propionic acid groups.

The products are

  • biliverdin (pronounce)
  • carbon monoxide (this is the only endogenous source of carbon monoxide)
  • iron (II)
  • NADP+

In the second biliverdin reductase reduces the central methene bridge of biliverdin, producing bilirubin.

Conversion of biliverdin to bilirubin requires NADPH as a reducing agent.

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