• Journal of Plant Biotechnology
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• v.32 no.1
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• pp.63-71
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• 2005

A cell-free enzyme solution prepared from suspension cultured cells of Phaseolus vulgaris successfully mediated conversions of cholesterol $\to$ cholestanol and 6-deoxo-28-norteasterone $\leftrightarrow$ 6-deoxo-28-nor-3-dehydroteasterone $\leftrightarrow$ 6-deoxo-28-nortyphasterol $\to$ 6-deoxo-28-norcastasterone $\to$ 28-norcastasterone. Al-though conversion of cholestanol to 6-deoxo-28-norteasterone intermediated by 6-deoxo-28-norcathasterone was not demonstrated, this strongly suggests that a complete set of biosynthetic enzymes catalyzing reactions from cholesterol to 28-norcastasterone via 6-deoxo-28-nor type brassinosteroids is endogenously present in the cells, which demonstrates that a $C_{27}$ brassinosteroids biosynthetic pathway, namely the late C-6 oxidation for $C_{27}$ brassinosteroids, is operative in the cells. Additionally, the enzyme solution mediated conversion of 28-norcastasterone to castasterone in the presence of S-adenosyl-methionine and NADPH, providing that the $C_{27}$ brassinosteroids biosynthesis is an important route to generate castasterone in the cells. Together with our previous finding that castasterone can be biosynthesized by the same biosynthetic pathway in tomato, this study demonstrates that the $C_{27}$ brassinosteroids biosynthesis is a common alternative process to maintain endo-genous level of castasterone, an active $C_{28}$ brassinosteroid, in plants.

• Bulletin of the Korean Chemical Society
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• v.31 no.6
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• pp.1782-1784
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• 2010

• Journal of Plant Biotechnology
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• v.34 no.3
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• pp.243-251
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• 2007

It has been recently demonstrated the presence of not only $C_{28}-BRs$ biosysnthesis, but also $C_{27}-$ and $C_{29}-BRs$ biosynthesis in plants, suggesting that BRs biosynthesis are complicatedly connected to produce biologically active BR (s). This prompted us to investigation of metabolism of a $C_{29}-BR$, 28-homoCS in seedlings of rice from which $C_{29}-BRs$ such as 28-homoTE and 28-homoTY have been identified. In vitro enzyme conversion study using a crude enzyme solution prepared from rice seedlings revealed that 28-homoCS is converted into both CS and 26-nor-28-homoCS, but their reversed reaction did not occur. This indicated that 28-homoCS is biosynthetically converted into more biologically active $C_{28}-BR$, CS by C-28 demethylation and biodegraded into 26-nor-28-homoCS by C-26 demethylation. Next, bio-conversion of 28-homoCS to 28-homoBL was examined by the same enzyme solution. No 28-homoBL as a metabolite of 28-homoCS was detected, meaning that biosynthetic reaction for 28-homoCS to 28-homoBL is not contained, and main connection of $C_{28}-BRs$ and $C_{29}-BRs$ biosynthesis is between CS and 28-homoCS in the rice seedling. This study is the first demonstrated that $C_{29}-BRs$ and $C_{28}-BRs$ bionsynthetic pathways are connected, and that $C_{29}-BRs$ biosynthetic pathway is an alternative biosynthetic pathway to produce more biologically active $C_{28}-BR$, CS in plant.