Sandmann Gerhard, Mautz Jürgen, Breitenbach Jürgen
Z Naturforsch C J Biosci. 2016 Sep 1;71(9-10):303-311. doi: 10.1515/znc-2016-0117.
In Nostoc PCC 7120, two different ketolases, CrtW and CrtO are involved in the formation of keto carotenoids from β-carotene. In contrast to other cyanobacteria, CrtW catalyzes the formation of monoketo echinenone whereas CrtO is the only enzyme for the synthesis of diketo canthaxanthin. This is the major photo protective carotenoid in this cyanobacterium. Under high-light conditions, basic canthaxanthin formation was transcriptionally up-regulated. Upon transfer to high light, the transcript levels of all investigated carotenogenic genes including those coding for phytoene synthase, phytoene desaturase and both ketolases were increased. These transcription changes proceeded via binding of the transcription factor NtcA to the promoter regions of the carotenogenic genes. The binding was absolutely dependent on the presence of reductants and oxo-glutarate. Light-stimulated transcript formation was inhibited by DCMU. Therefore, photosynthetic electron transport is proposed as the sensor for high-light and a changing redox state as a signal for NtcA binding.
在集胞藻PCC 7120中，两种不同的酮醇酶CrtW和CrtO参与了从β-胡萝卜素形成酮类胡萝卜素的过程。与其他蓝细菌不同，CrtW催化单酮类海胆酮的形成，而CrtO是合成双酮类角黄素的唯一酶。这是这种蓝细菌中的主要光保护类胡萝卜素。在高光条件下，碱性角黄素的形成在转录水平上被上调。转移到高光条件后，所有研究的类胡萝卜素生成基因的转录水平都增加了，包括编码八氢番茄红素合酶、八氢番茄红素去饱和酶和两种酮醇酶的基因。这些转录变化是通过转录因子NtcA与类胡萝卜素生成基因的启动子区域结合而发生的。这种结合绝对依赖于还原剂和氧代戊二酸的存在。光刺激的转录形成受到二氯苯基二甲基脲（DCMU）的抑制。因此，光合电子传递被认为是高光的传感器，而不断变化的氧化还原状态是NtcA结合的信号。
