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

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

The products are

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