Novel Metabolism of 1,25-Dihydroxyvitamin D3 with C24-C25 Bond Cleavage Catalyzed by Human CYP24A1
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- 作者：Natsumi Sawada ; Tatsuya Kusudo ; Toshiyuki Sakaki ; Susumi Hatakeyama ; Makoto Hanada ; Daisuke Abe ; Maya Kamao ; Toshio Okano ; Miho Ohta ; and Kuniyo Inouye
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：April 20, 2004
- 年：2004
- 卷：43
- 期：15
- 页码：4530 - 4537
- 全文大小：160K
- 年卷期：v.43,no.15(April 20, 2004)
- ISSN：1520-4995
文摘
Our previous study revealed that human CYP24A1 catalyzes a remarkable metabolism consistingof both C-23 and C-24 hydroxylation pathways that used both 25(OH)D3 and 1
,25(OH)2D3 as substrates,while rat CYP24A1 showed extreme predominance of the C-24 over C-23 hydroxylation pathway [Sakaki,T., Sawada, N., Komai, K., Shiozawa, S., Yamada, S., Yamamoto, K., Ohyama, Y. and Inouye, K. (2000)Eur. J. Biochem. 267, 6158-6165]. In this study, by using the Escherichia coli expression system forhuman CYP24A1, we identified 25,26,27-trinor-23-ene-D3 and 25,26,27-trinor-23-ene-1(OH)D3 as novelmetabolites of 25(OH)D3 and 1,25(OH)2D3, respectively. These metabolites appear to be closely relatedto the C-23 hydroxylation pathway, because human CYP24A1 produces much more of these metabolitesthan does rat CYP24A1. We propose that the C24-C25 bond cleavage occurs by a unique reactionmechanism including radical rearrangement. Namely, after hydrogen abstraction of the C-23 position of1,25(OH)2D3, part of the substrate-radical intermediate is converted into 25,26,27-trinor-23-ene-1(OH)D3, while a major part of them is converted into 1,23,25(OH)3D3. Because the C24-C25 bond cleavageabolishes the binding affinity of 1,25(OH)D3 for the vitamin D receptor, this reaction is quite effectivefor inactivation of 1,25(OH)D3.
,25(OH)2D3 as substrates,while rat CYP24A1 showed extreme predominance of the C-24 over C-23 hydroxylation pathway [Sakaki,T., Sawada, N., Komai, K., Shiozawa, S., Yamada, S., Yamamoto, K., Ohyama, Y. and Inouye, K. (2000)Eur. J. Biochem. 267, 6158-6165]. In this study, by using the Escherichia coli expression system forhuman CYP24A1, we identified 25,26,27-trinor-23-ene-D3 and 25,26,27-trinor-23-ene-1(OH)D3 as novelmetabolites of 25(OH)D3 and 1,25(OH)2D3, respectively. These metabolites appear to be closely relatedto the C-23 hydroxylation pathway, because human CYP24A1 produces much more of these metabolitesthan does rat CYP24A1. We propose that the C24-C25 bond cleavage occurs by a unique reactionmechanism including radical rearrangement. Namely, after hydrogen abstraction of the C-23 position of1,25(OH)2D3, part of the substrate-radical intermediate is converted into 25,26,27-trinor-23-ene-1(OH)D3, while a major part of them is converted into 1,23,25(OH)3D3. Because the C24-C25 bond cleavageabolishes the binding affinity of 1,25(OH)D3 for the vitamin D receptor, this reaction is quite effectivefor inactivation of 1,25(OH)D3.