Scaling laws in enzyme function reveal a new kind of biochemical universality

All life on Earth is unified by its use of a shared set of component chemical compounds and reactions, providing a detailed model for universal biochemistry. However, this notion of universality is specific to currently observed biochemistry and does not allow quantitative predictions about examples not yet observed. Here we introduce a more generalizable concept of biochemical universality, more akin to the kind of universality discussed in physics. Using annotated genomic datasets including an ensemble of 11955 metagenomes and 1282 archaea, 11759 bacteria and 200 eukaryotic taxa, we show how four of the major enzyme functions - the oxidoreductases, transferases, hydrolases and ligases - form universality classes with common scaling behavior in their relative abundances observed across the datasets. We verify these universal scaling laws are not explained by the presence of compounds, reactions and enzyme functions shared across all known examples of life. We also demonstrate how a consensus model for the last universal common ancestor (LUCA) is consistent with predictions from these scaling laws, with the exception of ligases and transferases. Our results establish the existence of a new kind of biochemical universality, independent of the details of the component chemistry, with implications for guiding our search for missing biochemical diversity on Earth, or other for any biochemistries that might deviate from the exact chemical make-up of life as we know it, such as at the origins of life, in alien environments, or in the design of synthetic life.