Primary metabolism in cyanobacteria is built on the Calvin-Benson-Bassham (CBB) cycle, oxidative pentose phosphate (OPP) pathway, Embden–Meyerhof–Parnas (EMP) pathway, and the tricarboxylic acid (TCA) cycle. Phosphoketolase (Xpk), commonly found in cyanobacteria, is an enzyme that is linked to all these pathways. However, little is known about its physiological role. Here, we show that most of the cyanobacterial Xpk surveyed are inhibited by ATP, and both copies of Xpk in nitrogen-fixing Cyanothece ATCC51142 are further activated by ADP, suggesting their role in energy regulation. Moreover, Xpk in Synechococcus elongatus PCC7942 and Cyanothece ATCC51142 show that their expressions are dusk-peaked, suggesting their roles in dark conditions. Finally, we find that Xpk in S. elongatus PCC7942 is responsible for survival using ATP produced from the glycogen-to-acetate pathway under dark, anaerobic condition. Interestingly, under this condition, xpk deletion causes glucose secretion in response to osmotic shock such as NaHCO₃, KHCO₃ and NaCl as part of incomplete glycogen degradation. These findings unveiled the role of this widespread enzyme and open the possibility for enhanced glucose secretion from cyanobacteria.

蓝藻的主要代谢建立在 Calvin-Benson-Bassham (CBB) 循环、氧化戊糖磷酸 (OPP) 途径、Embden-Meyerhof-Parnas (EMP) 途径和三羧酸 (TCA) 循环上。磷酸酮醇酶 (Xpk) 常见于蓝细菌中，是一种与所有这些途径相关的酶。然而，人们对其生理作用知之甚少。在这里，我们发现大多数被调查的蓝藻 Xpk 被 ATP 抑制，并且固氮Cyanothece ATCC51142 中的两个 Xpk 拷贝都被 ADP 进一步激活，表明它们在能量调节中的作用。此外，细长聚球藻PCC7942 和Cyanothece 中的XpkATCC51142 显示它们的表情在黄昏时达到峰值，表明它们在黑暗条件下的作用。最后，我们发现S. elongatus PCC7942 中的 Xpk 负责在黑暗、厌氧条件下使用从糖原到乙酸途径产生的 ATP 生存。有趣的是，在这种情况下，作为不完全糖原降解的一部分， xpk缺失会导致葡萄糖分泌以响应渗透压休克，例如 NaHCO ₃、KHCO _{3和 NaCl。}这些发现揭示了这种广泛存在的酶的作用，并开启了增强蓝藻葡萄糖分泌的可能性。