N-15 metabolic labeling of mammalian tissue with slow protein turnover

We previously reported the metabolic N-15 labeling of a rat where enrichment ranged from 94% to 74%. We report here an improved labeling strategy which generates 94% N-15 enrichment throughout all tissues of the rat. A high N-15 enrichment of the internal standard is necessary for accurate quantitation, and thus, this approach will allow quantitative mass spectrometry analysis of animal models of disease targeting any tissue.