tailieunhanh - Báo cáo Y học: The reactivity of a-hydroxyhaem and verdohaem bound to haem oxygenase-1 to dioxygen and sodium dithionite

Recently we have shown that ferrica-hydroxyhaem bound tohaemoxygenase-1 canbe converted to ferrous verdohaem by approximately an equimolar amount ofO2in the absence of exogenous electrons [Sakamoto,H.,Omata,Y.,Palmer, G.,and Noguchi, M. (1999)J. Biol. – 18200]. Contrary to those results,other studies have claimed that the conversion requires both O2andanelectron. | Eur. J. Biochem. 269 5231-5239 2002 FEBS 2002 doi The reactivity of a-hydroxyhaem and verdohaem bound to haem oxygenase-1 to dioxygen and sodium dithionite Hiroshi Sakamoto1 Yoshiaki Omata1. Shunsuke Havashi1. Saori Harada1 Graham Palmer2 and Masato Noguchi1 1 Department of Medical Biochemistry Kurume University School of Medicine Japan department of Biochemistry and Cell Biology Rice University Houston Texas USA Recently we have shown that ferric a-hydroxyhaem bound to haem oxygenase-1 can be converted to ferrous verdohaem by approximately an equimolar amount of O2 in the absence of exogenous electrons Sakamoto He dnata Y. Palmer G. add ĨQggucliM M. 1999 J. Biol. Chem. 274 1816618200 . Contrary to those results other studies have Haimed that the conversion requires both O2 and an electron. More recently Might et al. have reported that the major reaction product of ferric a-hydroxyhaem with O2 is a ferric porphyrin cation radical that can be converted to ferrous a-hydroxyhaem with sodium ditcioaite Migita c. T Fujii H. Mateaa K. M. Takahdihi. Sc Zhou n. and Yoshida. T. 19999 Biochim. Biophys. Acta 1432 203-213. To darify the reason s9 for the discrepancy we compared the rertctions . a-hydroxyhaem to verdohaem and verdohaem to bili-verdin under various conditions as well as according to the procedures of Migita. We hnd that complex formation of a-hydroxyhaem with haem oxygenase may be small and a substantial amount of free a-hydroxyhaem may remain depending on the reconstitution conditions this could lead to a misinterpretation of the experimental results. We also hnd that ferrous verdohaem appears to be air-sensitive and is therefore easily converted to a further oxidized species with excess O2. Finally we Íind hau di ì th Í on ì ee sems to he ídap-propriate for investigating the haem oxygenase reaction because it reduces ferrous verdohaem to a further reduced species that has not been seen in the haem degradation system driven .