¹⁵N nuclear magnetic resonance of living cells

Abstract

DIRECT observation of nuclear magnetic resonance (NMR) signals in living tissues, cells, or in their paniculate components is an appealing aspect of NMR spectroscopy as it further extends its applicability from the chemical to the biological domain. Of the various nuclei available for NMR studies, ¹H (refs 1–3), ¹³C (refs 2 and 4) and ³¹P (ref. 5) have already been observed in complex biological systems. The potential of the technique for the study of dynamic metabolic processes, or, eventually, aspects of cellular physiological changes, has been demonstrated^6,7. No other spectroscopy affords the resolution and direct interpretability in terms of chemical functional groups that NMR provides. One drawback is its relative insensitivity, especially when the representative nuclides of biological interest occur in low natural abundance, for example, ¹³C, ¹⁵N. In the case of ¹³C, isotopic enrichment from suitably labelled precursors has been shown to provide most valuable metabolic data in whole cell investigations⁶. There seem however, to be no studies of this type using nitrogen NMR. The relevance of nitrogen as a fundamental element of the constitutive building blocks of lipids, nucleic acids, proteins, and even some sugars, suggests that its direct observability in cells should provide an important probe to monitor the dynamics and control of its in vivo fixation and metabolism. We report here some results showing that ¹⁵N-NMR signals can be directly observed in whole, living cells.