Biliverdin is a product of the catabolism of heme (Figure 21.31). Amino acids released from the globin portion of the hemoglobin molecule are catabolized or reused for protein synthesis. The heme portion undergoes degradation, starting with a mixed-function oxidase reaction that opens the ring and converts one of the methene bridge carbons to carbon monoxide. Iron is released from the resulting linear tetrapyrrole, called biliverdin, and is transported to storage pools in bone marrow for reuse in erythrocyte production. The tetrapyrrole is next reduced to bilirubin, which is excreted.

1. Porphyrin and Chlorophyll Metabolism

2. Photosynthetic Pigments