NMR-based metabolite studies with (15)N amino acids

(15)N labeled amino acids are routinely used to label proteins or nucleic acids for study by NMR. However, NMR studies of (15)N labeled amino acids in metabolite studies have not been pursued extensively, presumably due to line broadening present under standard experimental conditions. In this work, we show that lowering the temperature to −5 °C allows facile characterization of (15)N-labeled amino acids. Further, we show that this technique can be exploited to measure (15)NH(3) produced in an enzyme catalyzed reaction and the transport and metabolism of individual amino acids in mammalian cell culture. With respect to (13)C-labeled amino acids, (15)N-labeled amino acids are less costly and enable direct characterization of nitrogen metabolism in complex biological systems by NMR. In summary, the present work significantly expands the metabolite pools and their reactions for study by NMR.