Metabolites once considered solely in catabolism or anabolism turn out to have key regulatory functions. Among these, the citric acid cycle intermediate succinate stands out owing to its multiple roles in disparate pathways, its dramatic concentration changes and its selective cell release. Here we propose that succinate has evolved as a signaling modality because its concentration reflects the coenzyme Q (CoQ) pool redox state, a central redox couple confined to the mitochondrial inner membrane. This connection is of general importance because CoQ redox state integrates three bioenergetic parameters: mitochondrial electron supply, oxygen tension and ATP demand. Succinate, by equilibrating with the CoQ pool, enables the status of this central bioenergetic parameter to be communicated from mitochondria to the rest of the cell, into the circulation and to other cells. The logic of this form of regulation explains many emerging roles of succinate in biology, and suggests future research questions.

曾经仅在分解代谢或合成代谢中被认为具有关键调节功能的代谢物。其中，柠檬酸循环中间体琥珀酸盐因其在不同途径中的多重作用、显着的浓度变化和选择性细胞释放而脱颖而出。在这里，我们提出琥珀酸盐已经进化为一种信号传导方式，因为它的浓度反映了辅酶 Q (CoQ) 池氧化还原状态，一种局限于线粒体内膜的中央氧化还原对。这种联系具有普遍重要性，因为 CoQ 氧化还原状态整合了三个生物能量参数：线粒体电子供应、氧张力和 ATP 需求。琥珀酸盐通过与辅酶 Q 池平衡，使这一中心生物能量参数的状态能够从线粒体传递到细胞的其余部分，进入循环和其他细胞。这种调节形式的逻辑解释了琥珀酸在生物学中的许多新兴作用，并提出了未来的研究问题。