偽枝藻素

偽枝藻素
	IUPAC名; (3E,3'E)-3,3'-bis(4-hydroxybenzylidene)-[1,1'-bi(cyclopenta[b]indole)]-2,2'(3H,3'H)-dione
別名	Scytonemin
識別
CAS號	152075-98-4
性質
化學式	C36H20N2O4
摩爾質量	544.6 g/mol g·mol⁻¹
外觀	brown solid
溶解性	25mg/ml DMSO
λmax	325-425nm nm
	若非註明，所有數據均出自標準狀態（25 ℃，100 kPa）下。

偽枝藻素（英語：Scytonemin）是一種生物色素，由許多藍細菌合成，包括Calothrix sp.^[2]、Lyngbya aestuarii^[3]等，最早在1849被人發現，但直到1993年才解析了其結構^[4]。據信，偽枝藻素對細菌起到了防曬油的作用，在325-425 nm的有很大的吸收峰，並在250 nm的紫外波段有個獨立的吸收峰^[4]，在暴露在紫外線的情況下才啟動它的生物合成^[5]。

生物合成

在 Lyngbya aestuarii 體內的偽枝藻素生物合成途徑最近由 Balskus、Case和Walsh 發現。它起始於L-色氨酸到3-吲哚丙酮酸的轉化，之後再與對羥基苯丙酮酸結合。產物的β-酮酸基再發生環化形成帶羰基的三環化合物，之後再氧化二聚化形成偽枝藻素，三個反應步驟依次由ScyB、ScyA、ScyC催化，如下圖所示^[3]：

參考文獻

^ Scytonemin CAS (152075-98-4). Santa Cruz Biotechnology, Inc. [2011-05-30]. （原始內容存檔於2011-10-02）.
^ Dillon, Jesse G.; Castenholz, Richard W. The synthesis of the UV-screening pigment, scytonemin, and photosynthetic performance in isolates from closely related natural populations of cyanobacteria (Calothrix sp.). Environmental Microbiology. 2003, 5 (6): 484–91. PMID 12755715. doi:10.1046/j.1462-2920.2003.00436.x.
^ ^3.0 ^3.1 ^3.2 Balskus, Emily P.; Case, Rebecca J.; Walsh, Christopher T. The biosynthesis of cyanobacterial sunscreen scytonemin in intertidal microbial mat communities. FEMS Microbiology Ecology. 2011: 1–11. doi:10.1111/j.1574-6941.2011.01113.x.
^ ^4.0 ^4.1 Proteau, P. J.; Gerwick, W. H.; Garcia-Pichel, F.; Castenholz, R. The structure of scytonemin, an ultraviolet sunscreen pigment from the sheaths of cyanobacteria. Experientia. 1993, 49 (9): 825–9. PMID 8405307. doi:10.1007/BF01923559.
^ M. Bandaranayake, Wickramasinghe. Mycosporines: are they nature’s sunscreens?. Natural Product Reports. 1998, 15 (2): 159–72. PMID 9586224. doi:10.1039/A815159Y.

外部連結

Balskus, Emily P.; Case, Rebecca J.; Walsh, Christopher T. The biosynthesis of cyanobacterial sunscreen scytonemin in intertidal microbial mat communities. FEMS Microbiology Ecology. 2011: no–no. doi:10.1111/j.1574-6941.2011.01113.x.

[1] Scytonemin CAS (152075-98-4). Santa Cruz Biotechnology, Inc. [2011-05-30]. （原始內容存檔於2011-10-02）.

[2] Dillon, Jesse G.; Castenholz, Richard W. The synthesis of the UV-screening pigment, scytonemin, and photosynthetic performance in isolates from closely related natural populations of cyanobacteria (Calothrix sp.). Environmental Microbiology. 2003, 5 (6): 484–91. PMID 12755715. doi:10.1046/j.1462-2920.2003.00436.x.

[pmid21501195-3] 3.0 ^3.1 ^3.2 Balskus, Emily P.; Case, Rebecca J.; Walsh, Christopher T. The biosynthesis of cyanobacterial sunscreen scytonemin in intertidal microbial mat communities. FEMS Microbiology Ecology. 2011: 1–11. doi:10.1111/j.1574-6941.2011.01113.x.

[pmid8405307-4] 4.0 ^4.1 Proteau, P. J.; Gerwick, W. H.; Garcia-Pichel, F.; Castenholz, R. The structure of scytonemin, an ultraviolet sunscreen pigment from the sheaths of cyanobacteria. Experientia. 1993, 49 (9): 825–9. PMID 8405307. doi:10.1007/BF01923559.

[5] M. Bandaranayake, Wickramasinghe. Mycosporines: are they nature’s sunscreens?. Natural Product Reports. 1998, 15 (2): 159–72. PMID 9586224. doi:10.1039/A815159Y.

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