Structural Study of Enzymes Involved in Porphyrin Metabolism

Porphyrin derivatives including hemes and chlorophylls are indispensable for all organisms because they are involved in respiration, photosynthesis, and various enzymatic reactions. However, because excess free heme is toxic for organisms, heme metabolism is important to reduce oxidative stress produced by excess heme. Heme and bilin metabolism are also crucial for photosynthetic organisms because the metabolites, bilin pigments, are utilized for photosynthesis and photoreception. In this review, our structural study of enzymes involved in heme and bilin metabolisms is summarized. Especially, molecular interaction between heme oxygenase and NADPH-cytochrome P450 reductase and the reaction mechanism of ferredoxin-dependent bilin reductases are discussed.