Water, the most abundant compound on the surface of the Earth and probably in the universe, is the medium of biology, but is much more than that. Water is the most frequent actor in the chemistry of metabolism. Our quantitation here reveals that water accounts for 99.4% of metabolites in Escherichia coli by molar concentration. Between a third and a half of known biochemical reactions involve consumption or production of water. We calculated the chemical flux of water and observed that in the life of a cell, a given water molecule frequently and repeatedly serves as a reaction substrate, intermediate, cofactor, and product. Our results show that as an E. coli cell replicates in the presence of molecular oxygen, an average in vivo water molecule is chemically transformed or is mechanistically involved in catalysis ~ 3.7 times. We conclude that, for biological water, there is no distinction between medium and chemical participant. Chemical transformations of water provide a basis for understanding not only extant biochemistry, but the origins of life. Because the chemistry of water dominates metabolism and also drives biological synthesis and degradation, it seems likely that metabolism co-evolved with biopolymers, which helps to reconcile polymer-first versus metabolism-first theories for the origins of life.

水是地球表面乃至宇宙中最丰富的化合物，是生物的媒介，但其意义远不止于此。水是新陈代谢化学中最常见的参与者。我们的定量结果显示，按摩尔浓度计算，水占大肠杆菌代谢物的 99.4% 。三分之一到一半的已知生化反应涉及水的消耗或产生。我们计算了水的化学通量，并观察到在细胞的生命周期中，给定的水分子频繁且重复地充当反应底物、中间体、辅因子和产物。我们的结果表明，当大肠杆菌细胞在分子氧存在下复制时，体内水分子平均发生化学转化或机械参与催化约 3.7 次。我们的结论是，对于生物水来说，介质和化学参与者之间没有区别。水的化学转化不仅为理解现存的生物化学，而且为理解生命的起源提供了基础。由于水的化学性质主导着新陈代谢，也驱动生物合成和降解，因此新陈代谢似乎与生物聚合物共同进化，这有助于调和生命起源的聚合物优先理论与代谢优先理论。