The recent discovery of the Entner-Doudoroff (ED) pathway as a third glycolytic route beside Embden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (OPP) pathway in oxygenic photoautotrophs requires a revision of their central carbohydrate metabolism. In this study, unexpectedly, we observed that deletion of the ED pathway alone, and even more pronounced in combination with other glycolytic routes, diminished photoautotrophic growth in continuous light in the cyanobacterium Synechocystis sp. PCC 6803. Furthermore, we found that the ED pathway is required for optimal glycogen catabolism in parallel to an operating Calvin–Benson–Bassham (CBB) cycle. It is counter-intuitive that glycolytic routes, which are a reverse to the CBB cycle and do not provide any additional biosynthetic intermediates, are important under photoautotrophic conditions. However, observations on the ability to reactivate an arrested CBB cycle revealed that they form glycolytic shunts that tap the cellular carbohydrate reservoir to replenish the cycle. Taken together, our results suggest that the classical view of the CBB cycle as an autocatalytic, completely autonomous cycle that exclusively relies on its own enzymes and CO2 fixation to regenerate ribulose-1,5-bisphosphate for Rubisco is an oversimplification. We propose that in common with other known autocatalytic cycles, the CBB cycle likewise relies on anaplerotic reactions to compensate for the depletion of intermediates, particularly in transition states and under fluctuating light conditions that are common in nature.

Entner-Doudoroff（ED）途径作为氧光养生物中除Embden-Meyerhof-Parnas（EMP）和氧化戊糖磷酸（OPP）途径之外的第三种糖酵解途径的最新发现需要对其中心碳水化合物的代谢进行修订。在这项研究中，出乎意料的是，我们观察到单独的ED途径缺失，以及与其他糖酵解途径的结合更为明显，从而减少了蓝藻集胞藻在连续光照下的光自养生长。sp。PCC6803。此外，我们发现ED途径是最佳的糖原分解代谢所必需的，与运作的Calvin-Benson-Bassham（CBB）循环平行。在光养养条件下，与CBB循环相反且不提供任何其他生物合成中间体的糖酵解途径很重要，这是违反直觉的。但是，对重新激活已停止的CBB循环的能力的观察表明，它们形成了糖酵解分流，可利用细胞中的碳水化合物储集层补充循环。综上所述，我们的研究结果表明，将CBB循环视为完全依赖于自身酶和CO2固定来再生Rubisco-1,5-双磷酸核糖的自动催化，完全自主循环的经典观点过于简单化了。