Abstract: Described is a method for analyzing the metabolites of a biological sample which comprises quantitatively determining one or more metabolites in said sample in a way that said quantitative determination resolves isotopic mass differences within one metabolite, said method being characterized in that the sample comprises or is derived from a cell which has been maintained under conditions allowing the uptake of an isotopically labeled metabolizable compound so that the metabolites in said cell are saturated with the isotope with which said metabolizable compound is labeled. This method may further comprise, prior to quantitative determining the metabolites, combining the biological sample (i.e. the first biological sample) with a second biological sample in which the metabolites are not isotopically labeled or are isotopically labeled differently from the first biological sample; and determining in said biological samples the relative quantity of metabolites which differ by their isotopical label.

Abstract: Described is a method for determining the function of a gene. This method involves determining the amount of transcript for each of a set of candidate genes in samples taken from different phenotypic and/or genotypic states of an organism and determining the amount of each of a plurality of metabolites in different samples taken from the same states as those mentioned above. Subsequently, the data obtained is analyzed by suitable mathematical methods in order to identify a transcript and metabolites which correlate in the different states, thereby identifying a transcript corresponding to a gene which influences the amount of metabolites in the organism. Furthermore described is a method for identifying a gene which is capable of modifying the amount of a metabolite in an organism and to a method for identifying a metabolite which is capable of modifying the amount of a transcript in an organism. Likewise, uses of the genes and metabolites identified in the aforementioned methods are described.

Abstract: Described is a method for analysing the metabolites of a biological sample which comprises quantitatively determining one or more metabolites in said sample in a way that said quantitative determination resolves isotopic mass differences within one metabolite, said method being characterized in that the sample comprises or is derived from a cell which has been maintained under conditions allowing the uptake of an isotopically labeled metabolizable compound so that the metabolites in said cell are saturated with the isotope with which said metabolizable compound is labeled. This method may further comprise, prior to quantitative determining the metabolites, combining the biological sample (i.e. the first biological sample) with a second biological sample in which the metabolites are not isotopically labeled or are isotopically labeled differently from the first biological sample; and determining in said biological samples the relative quantity of metabolites which differ by their isotopical label.