Nature Metabolism, Published online: 29 April 2026; doi:10.1038/s42255-026-01519-7Nitrogen metabolism is more complex and less mapped than carbon pathways owing to the diversity of nitrogen sources and disjointed routing. Savani et al. develop a multiplexed nitrogen labelling platform to trace system-wide nitrogen flows, revealing how undifferentiated and mature cells select nitrogen sources for pyrimidine nucleotide synthesis.
