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Aldo-keto reductase 1B1 and 1B3 (AKR1B1 and AKR1B3) are the pri-mary human and mouse prostaglandin F2a(PGF2a) synthases, respectively, which catalyze the NADPH-dependent reduction of PGH2, a common intermediate of various prostanoids, to form PGF2a. In this study, we found that AKR1B1 and AKR1B3, but not AKR1B7 and AKR1C3, also catalyzed the isomerization of PGH2 to PGD2 in the absence of NADPH or NADP + . | 1FEBS Journal Catalytic mechanism of the primary human prostaglandin F2a synthase aldo-keto reductase 1B1 - prostaglandin D2 synthase activity in the absence of NADP H Nanae Nagata1 Yukiko Kusakari2 Yoshifumi Fukunishi3 Tsuyoshi Inoue2 and Yoshihiro Urade1 1 Department of Molecular BehavioralBiology Osaka Bioscience Institute Japan 2 Department of Materials Chemistry Osaka University Japan 3 BiomedicinalInformation Research Center NationalInstitute of Advanced IndustrialScience and Technology Tokyo Japan Keywords aldo-keto reductase His prostaglandin D2 synthase prostaglandin F2a synthase prostaglandin H2 Correspondence Y. Urade Department of Molecular BehavioralBiology Osaka Bioscience Institute 6-2-4 Furuedai Suita Osaka 565-0874 Japan Fax 81 6 6872 2841 Tel 81 6 6872 4851 E-mail uradey@obi.or.jp Received 21 October 2010 revised 1 February 2011 accepted 7 February 2011 doi 10.1111 j.1742-4658.2011.08049.x Aldo-keto reductase 1B1 and 1B3 AKR1B1 and AKR1B3 are the primary human and mouse prostaglandin F2a PGF2a synthases respectively which catalyze the NADPH-dependent reduction of PGH2 a common intermediate of various prostanoids to form PGF2a. In this study we found that AKR1B1 and AKR1B3 but not AKR1b7 and AKR1C3 also catalyzed the isomerization of PGH2 to PGD2 in the absence of NADPH or NADP . Both PGD2 and PGF2a synthase activities of AKR1B1 and AKR1B3 completely disappeared in the presence of NADP or after heat treatment of these enzymes at 100 C for 5 min. The Km Vmax pK and optimum pH values of the PGD2 synthase activities of AKR1B1 and AKR1B3 were 23 and 18 IM 151 and 57 nmol-min-1 mg protein -1 7.9 and 7.6 and pH 8.5 for both AKRs respectively and those of PGF2a synthase activity were 29 and 33 IM 169 and 240 nmol-min-1 mg protein -1 6.2 and 5.4 and pH 5.5 and pH 5.0 respectively in the presence of 0.5 mM NADPH. Site-directed mutagenesis of the catalytic tetrad of AKR1B1 composed of Tyr Lys His and Asp revealed that the triad of Asp43 Lys77 and His110 but
