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. 2016 Apr 6;146(5):957–963. doi: 10.3945/jn.116.230078

FIGURE 1.

FIGURE 1

NR is stable in milk and is degraded by S. aureus. (A) Stability of [18O]-NR in 4 store-bought brands of skim milk and in water at pH 5, 7, and 11 (n = 3) was assessed with LC-MS/MS. NR metabolism by S. aureus was determined with [13C1, D1]-NR and LC-MS (B–H). (B–F) Extracellular concentration of [13C1, D1]-NR, nonlabeled Nam, [13C1]-Nam, nonlabeled NA, and [13C1]-NA in Todd-Hewitt + 50 mmol/L Bis-Tris (pH 6.7) media containing 10 μmol/L [13C1, D1]-NR incubated at 37°C without or with S. aureus RN3170 inoculation (n = 3 for inoculated media). In each panel, the concentration of the metabolite is shown in the noninoculated media (n = 1). (G) Intracellular concentration of endogenous or 13C1 enriched Nam. (H) Intracellular concentration of endogenous 13C1-, or 13C1, D1–enriched NAD+ from extracts of S. aureus RN3170 cell pellets (n = 3/time point). For intracellular measurements, a Holm-Sidak multiple-comparisons post hoc test was performed to test for statistical significance compared with time point zero for each metabolite (B and G). For extracellular measurements, a Holm-Sidak multiple-comparisons test was performed to test for statistical significance compared with noninoculated medium within each time point (C–F and H). Data are represented as means ± SEMs. *P < 0.05, **P < 0.01, and ***P < 0.001. NA, nicotinic acid; Nam, nicotinamide; NR, nicotinamide riboside.