Substrate channeling is a widespread mechanism in metabolic pathways to avoid decomposition of unstable intermediates, competing reactions, and to accelerate catalytic turnover. During the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXα to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently converted by phycoerythrobilin:ferredoxin oxidoreductase to the final product phycoerythrobilin. Although substrate channeling has been postulated already a decade ago, detailed experimental evidence was missing. Using a new on-column assay employing immobilized enzyme in combination with UV-Vis and fluorescence spectroscopy revealed that both enzymes transiently interact and that transfer of the intermediate is facilitated by a significantly higher binding affinity of DHBV toward phycoerythrobilin:ferredoxin oxidoreductase. Concluding from the presented data, the intermediate DHBV is transferred via proximity channeling.

中文翻译：

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蓝藻藻红蛋白合成过程中的邻近通道。

底物通道化是代谢途径中一种广泛的机制，可避免不稳定的中间体分解，竞争性反应并加速催化转化。在蓝细菌中光捕获藻胆素的生物合成过程中，铁氧还蛋白依赖性胆红素还原酶的两个成员参与了将开环四吡咯比利弗丁IXα还原为粉红色色素藻红蛋白的过程。第一个反应被15,16-dihydrobiliverdin：ferredoxin氧化还原酶催化，产生不稳定的中间体15,16-dihydrobiliverdin（DHBV）。该中间体随后被藻红蛋白：铁氧还蛋白氧化还原酶转化为终产物藻红蛋白。尽管已经在十年前假定了基质通道，但是缺少详细的实验证据。使用结合固定化酶与UV-Vis和荧光光谱法的新的柱上检测方法，发现两种酶均会短暂相互作用，并且DHBV对藻红蛋白：铁氧还蛋白氧化还原酶的结合亲和力明显更高，从而促进了中间体的转移。从显示的数据得出结论，中间DHBV是通过邻近通道传输的。