Extended Data Fig. 6. Pterin profile for the demonstration of DHP substrate origins.

a, Previously described recycling and side-chain cleavage mechanism of biopterin in mammalian cells. Pterin and 7,8-dihydroxanthopterin (XPH₂) are known as break-down products of biopterin. Similarly, we observed pterin (m/z 164.0572) and XPH₂ (m/z 182.0678) in the BH₄ in vitro chemical reaction via hydrogenation of commercial BH₂ followed by aerobic incubation in water, not in the BH₂ solution. Besides, colipterins were detected in BH₄ solution supplemented with PP. Representatively, col327 (6) (m/z 328.1046) is shown. b, Upregulation of pterin and XPH₂ in E. coli Nissle1917 in response to the sub-lethal levels of SMX. Dose-responses of pterin and XPH₂ in antifolate SMX stress. The mean and s.d. (error bars) from three biological experiments (n = 3) are shown. Statistical significance was accessed using a two-tailed unpaired t-test. MS intensity of EIC chromatogram was determined by ion counts corresponding to pterin ([M+H]⁺ m/z 164.0572) and XPH₂ ([M+H]⁺ m/z 182.0678) within a 10 ppm error window. High-resolution ESI-QTOF-LC-MS spectra of samples were analyzed using Phenomenex Kinetex C₁₈ (100Å) 5 μm (250 × 4.6 mm) column with a gradient from 10%−100% aqueous acetonitrile in 0.1% formic acid over 30 min and with a 0.7 ml min⁻¹ flow rate.