Two Steps of Heme Degradation
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 reaction 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 reaction 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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Last modified 1/5/95