Figure 1

Aging-associated decline in heavy isotopic metabolites in yeast revealed by LC-MS-based metabolomics. See also Supplementary Figure S1, Supplementary Table S2. (a, b), The intracellular metabolome from yeast cells was examined by LC-MS when cells have reached stationary phase at day 3, 5, and 7 after inoculation (n=6 for each time point). The O2PLS-DA clustering for two strains (DBY746, W303) is shown for DBY746 in a (R2Y=0.983, Q2=0.979), and for W303 in b (R2Y=0.985, Q2=0.955). X and Y axis are reversed for clarity of comparison. (c, d) Contribution of individual metabolites to the clustering models in a, b, respectively. Each circle represents a metabolite (mass feature). All twenty proteinogenic amino acids and cysteine are highlighted in magenta. Our method does not distinguish isoleucine and leucine. (e) The plot of the intracellular levels of glutamine (Gln) in c, d. The P values of two-tailed unequal variance t-test are shown above each bar for comparison with levels at day 3 for each strain. Error bars=s.e.m. The same type t-test was applied in all other analyses in this manuscript unless otherwise noted. (f) The relative monoisotopic abundances of glutamine that contains one ¹³C, ²H (D) or ¹⁵N, respectively, normalized to the most abundant mass species composed of all light isotopes (n=6). Values were manually calculated in Thermo XCalibur. The t-test P values are shown above each bar for comparison with levels at day 3 for each strain. Dotted lines indicate the relative monoisotopic abundances of medium glutamine. Error bars=s.e.m. NS, not significant. (g) The levels of glutamine and its D-isotopic form in the culture medium in the first 3 days after inoculation for two strains (DBY746, BY4741, n=3 each). The t-test P values are shown above each bar for comparison with starting medium levels. Error bars =s.e.m.