Takaichi S, Mochimaru M
Department of Biology, Nippon Medical School, Kawasaki, 211-0063, Japan.
Cell Mol Life Sci. 2007 Oct;64(19-20):2607-19. doi: 10.1007/s00018-007-7190-z.
Cyanobacteria grow by photosynthesis, and necessarily contain chlorophyll and carotenoids, whose main functions are light harvesting and photoprotection. In this review, we discuss the carotenoids, carotenogenesis pathways, and characteristics of carotenogenesis enzymes and genes in some cyanobacteria, whose carotenogenesis enzymes have been functionally confirmed. In these cyanobacteria, various carotenoids have been identified, including the unique ketocarotenoids, echinenone and 4-ketomyxol; and the carotenoid glycosides, myxol glycosides and oscillol diglycosides. From these findings, certain carotenogenesis pathways can be proposed. The different compositions of carotenoids among these species might be due to the presence or absence of certain gene(s), or to different enzyme characteristics. For instance, two distinct beta-carotene ketolases, CrtO and CrtW, are properly used in two pathways depending on the species. One beta-carotene hydroxylase, CrtR, has been identified, and its substrate specificities vary across species. At present, functionally confirmed genes have been found in only a few species, and further studies are needed.
蓝藻通过光合作用生长，必然含有叶绿素和类胡萝卜素，其主要功能是捕光和光保护。在本综述中，我们讨论了一些蓝藻中的类胡萝卜素、类胡萝卜素合成途径以及类胡萝卜素合成酶和基因的特征，这些蓝藻的类胡萝卜素合成酶已得到功能确认。在这些蓝藻中，已鉴定出多种类胡萝卜素，包括独特的酮类胡萝卜素、海胆酮和4-酮粘胶醇；以及类胡萝卜素糖苷、粘胶醇糖苷和振荡醇二糖苷。基于这些发现，可以提出某些类胡萝卜素合成途径。这些物种之间类胡萝卜素组成的差异可能是由于某些基因的存在或缺失，或者是由于酶的特性不同。例如，两种不同的β-胡萝卜素酮酶CrtO和CrtW根据物种的不同在两条途径中被正确使用。已鉴定出一种β-胡萝卜素羟化酶CrtR，其底物特异性因物种而异。目前，仅在少数物种中发现了功能得到确认的基因，还需要进一步研究。
