Enzymes catalyze reactions in vivo at different rates and each enzyme molecule has a lifetime limit before it is degraded and replaced to enable catalysis to continue. Considering these rates together as a unitless ratio of catalytic cycles until replacement (CCR) provides a new quantitative tool to assess the replacement schedule of and energy investment into enzymes as they relate to function. Here, we outline the challenges of determining CCRs and new approaches to overcome them and then assess the CCRs of selected enzymes in bacteria and plants to reveal a range of seven orders of magnitude for this ratio. Modifying CCRs in plants holds promise to lower cellular costs, to tailor enzymes for particular environments, and to breed enzyme improvements for crop productivity.

酶以不同的速率在体内催化反应，每个酶分子在降解和替换以使其继续催化之前都有寿命限制。将这些速率一起考虑为直到置换（CCR）为止的催化循环的无单位比率，这提供了一种新的定量工具来评估酶的置换时间表和与功能有关的能源投资。在这里，我们概述了确定CCR的挑战和克服这些挑战的新方法，然后评估细菌和植物中选定酶的CCR，以揭示该比率的七个数量级范围。修饰植物中的CCR有望降低细胞成本，为特定环境定制酶，并为作物生产力培育酶。