カシバ　ミサト   加柴　美里    所属   学環 教養学環    職種   教授
言語種別	英語
発行・発表の年月	2023/07
形態種別	学術論文
査読	査読あり
標題	Riboflavin compounds show NAD(P)H dependent quinone oxidoreductase-like quinone reducing activity
執筆形態	共著
掲載誌名	J Clin Biochem Nutr
掲載区分	国外
出版社・発行元	J Clin Biochem Nutr
巻・号・頁	73(1),pp.52-60
著者・共著者	Midori Nagase, Miku Sakamoto, Sakiko Amekura, Sayaka Akiba, Misato Kashiba, Kenji Yokoyama, Yorihiro Yamamoto, Akio Fujisawa
概要	NAD(P)H-dependent quinone oxidoreductase (NQO) is an essential enzyme in living organisms and cells protecting them from oxidative stress. NQO reduces coenzyme Q (CoQ) using NAD(P)H as an electron donor. In the present study, we searched for coenzyme Q10 reducing activity from fractions of gel filtration-fractionated rat liver homogenate. In addition to the large-molecular-weight fraction containing NQO, CoQ10 reducing activity was also detected in a low-molecular-weight fraction. Furthermore, dicumarol, a conventional inhibitor of NQO1 (DT diaphorase), did not inhibit the reduction but quercetin did, suggesting that the activity was not due to NQO1. After further purification, the NADH-dependent CoQ10-reducing compound was identified as riboflavin. Riboflavin is an active substituent of other flavin compounds such as FAD and FMN. These flavin compounds also reduced not only CoQ homologues but also vitamin K homologues in the presence of NADH. The mechanism was speculated to work as follows: NADH reduces flavin compounds to the corresponding reduced forms, and subsequently, the reduced flavin compounds immediately reduce bio-quinones. Furthermore, the flavin-NADH system reduces CoQ10 bound with saposin B, which is believed to function as a CoQ transfer protein in vivo. This flavin-dependent CoQ10 reduction, therefore, may function in aqueous phases such as the cell cytosol and bodily fluids.