15N relaxation and quantification of 15N-labelled metabolites in cell extracts

Abstract

15N is useful for studying nitrogen metabolism by isotope labelling. However, the 15N NMR analysis is hampered by negative nOe factors and sometimes long T1 values. Moreover, these can have a marked dependency on their physico-chemical environment (pH, ionic charge, viscosity, etc.) making quantitative analysis of cell extracts from labelling experiments difficult. We have, therefore, analysed some of these dependencies in order to find conditions in which quantitative analysis of some major metabolites (amino acids, ammonium, nitrate, urea) can be performed reliably and with sufficient signal. © 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved.