15Nlabeled

15N labeling refers to the incorporation of the stable isotope nitrogen-15 into biomolecules in place of the more abundant nitrogen-14. This labeling is used to trace nitrogen-containing compounds in biological systems and to enhance the detection and analysis of molecules containing nitrogen, especially in spectroscopy and mass spectrometry. Researchers may pursue uniform labeling, where all nitrogens in a molecule or organism are enriched in 15N, or site-specific labeling, where only particular nitrogen sites are labeled through the use of labeled precursors or recombinant expression strategies.

Labeling is typically achieved by providing 15N-enriched nutrients to organisms or by synthesizing chemicals from 15N-labeled starting materials. Common 15N sources include 15NH4+ and 15NO3- in growth media for microbes, yeast, and plants, or 15N-labeled amino acids for controlled protein production. Commercial suppliers offer a range of 15N-labeled compounds for research purposes. Labeling efficiency depends on the organism, growth conditions, and the specific isotope source.

Analytical applications of 15N labeling are diverse. In nuclear magnetic resonance (NMR) spectroscopy, 15N provides a convenient spin-1/2 nucleus that enables heteronuclear experiments such as HSQC and HNCO, facilitating structural and dynamic studies of proteins and nucleic acids. Mass spectrometry can detect 15N incorporation by characteristic mass shifts, aiding quantitative proteomics and metabolic tracing. In metabolic studies, 15N tracers reveal nitrogen assimilation pathways and fluxes in cells, tissues, or ecosystems.

Limitations include cost, potential isotope effects on metabolism, and incomplete labeling. 15N labeling is generally considered safe and non-radioactive, though proper handling of labeled materials follows standard laboratory protocols.