Biochemical studies on cytochrome P450 monooxygenases in biosynthesis and catabolism of abscisic acid and plant steroids(The JSCRP Award for the Encouragement of Young Scientists, The Society Awards Lectures)

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  • Mizutani Masaharu
    Chemistry of Molecular Biocatalysts, Division of Biochemistry, Institute for Chemical Research, Kyoto University

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  • アブシシン酸および植物ステロイドの代謝系に関わるシトクロムP450の酵素化学的研究(奨励賞,受賞業績)
  • [植物化学調節学会]奨励賞 アブシシン酸および植物ステロイドの代謝系に関わるシトクロムP450の酵素化学的研究
  • ショクブツ カガク チョウセツ ガッカイ ショウレイショウ アブシシンサン オヨビ ショクブツ ステロイド ノ タイシャケイ ニ カカワル シトクロム P450 ノ コウソ カガクテキ ケンキュウ

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Abstract

Cytochrome P450 monoxygenases (P450s) are heme-containing membrane proteins and catalyze the monooxygenation reactions in a wide range of metabolic pathways of various bioactive substances. In this study, several plant P450s belonging to 85-clan and 710-clan were investigated by biochemical approaches. (1) CYP707As have been identified as a major ABA catabolic enzyme, ABA 8'-hydroxylase. A triazole-type growth retardant, uniconazole-P, was found to be a potent inhibitor of ABA 8'-hydroxylase, and the inhibitor treated plants showed enhanced drought tolerance because of ABA accumulation. (2) Enzymatic functions of CYP90A1, 90B1, 90C1, 90D1, and 724B1 involved in BR biosynthesis were clarified by using an in vitro assay reconstituted with the recombinant P450s expressed either in a baculovirus-insect cell system or in a bacterial-expression system, and these studies revealed that BRs are biosynthesized via the campestanol-independent pathway. (3) CYP710As were found to encode plant sterol C-22 desaturases. Arabidopsis CYP710A1/A3/A4 catalyze C-22 desaturation of β-sitosterol to produce stigmasterol, while CYP710A2 specifically C-22 desaturate 24-epi-campesterol to produce brassicasterol, which is a unique sterol in Brassica species.

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