SEARCH Articles Figures Tables 18<). isotopic labelling with Isotope isotopic labeling Isotope label Isotope-labelled Isotopes acids Isotopic labeling Isotopic labeling with Isotopic labelled Isotopic labelling Isotopic labels Isotopical labeling Labeling with Labelled with Labelled with isotopic Pyruvate/pyruvic acid Pyruvic acid Pyruvic acid labelled with