Inhibition of CMP-sialic acid transport by endogenous 5-methyl CMP
Fig 2
Comparison of mass spectra for buffer-only versus CST protein-containing samples.
A) Extracted ion chromatograms for an m/z of 338.0701 ± 0.5 were taken from the LC-MS runs in positive ESI mode (shown in Fig 2 –S1 Fig) and are shown for the buffer-only control (top) or the CST protein-containing sample (bottom). B-E) Mass spectra in either positive (panels B, C, and E) or negative (panel D) ESI modes are shown. Panels B-D show the spectra for the sample eluting from the HPLC column from between 10.7–10.8 min for the buffer-only control (B) or protein-containing samples (C and D). Panel E shows the spectrum for the buffer-only sample eluting from the HPLC column between 9.6–9.8 min. F) Tandem MS/MS was performed on the ion with m/z of 338.0722 from panel C, with a collision energy of 10 eV. A selection filter of 1.3 m/z was used. The black diamond indicates the position of the precursor ion. G) A putative scheme describes the fragmentation of m5CMP ([M+H]+ = 338.0748) to produce the most prominent ion (m/z of 126.0686) in the MS/MS spectrum shown in panel F.