2014 年 56 巻 6 号 p. 393-398
Heme is an important co-factor for several biological processes such as respiration, electron transfer and enzymatic reaction, whereas free heme is toxic because of the production of reactive oxygen species. Therefore free heme should be decomposed immediately in vivo. Heme oxygenase (HO) is an indispensable player for heme degradation. HO catalyzes the site-specific cleavage of heme porphyrin ring to produce biliverdin, ferrous iron, and carbon monoxide. This reaction requires several oxygen molecules and electrons supplied from NADPH-cytochrome P450 reductase (CPR). We have determined the crystal structure of the redox complex of CPR and HO. In this structure, FMN bound to CPR is close to heme bound to HO, whereas FAD bound to CPR is far from both of FMN and heme. Electron transfer mechanism from CPR to HO with dynamic conformation change of CPR is discussed.