TABLE 3.
Major monosodiated ions identified in the ESI Q-TOF-MS1 spectra of antibody- and Stx-detected neutral GSLs from human plasma and their proposed structures
| [M+Na]+, m/z Antibody-Detected | [M+Na]+, m/z Stx1-Detected | [M+Na]+, m/z Stx2-Detected | Proposed Structure |
|---|---|---|---|
| 856.58 | n.d | n.d. | Lc2Cer (d18:1, C14:0) |
| 884.59 | n.d. | n.d. | Lc2Cer (d18:1, C16:0) |
| 994.68 | n.d. | n.d. | Lc2Cer (d18:1, C24:1) |
| 1046.67 | 1046.67 | 1046.63 | Gb3Cer (d18:1, C16:0) |
| 1074.68 | 1074.71 | 1074.64 | Gb3Cer (d18:1, C18:0) |
| 1128.74 | 1128.75 | 1128.68 | Gb3Cer (d18:1, C22:1) |
| 1130.76 | 1130.91 | 1130.70 | Gb3Cer (d18:1, C22:0) |
| 1142.77 | 1142.78 | 1142.75 | Gb3Cer (d18:1, C23:1) |
| 1144.77 | 1144.78 | 1144.75 | Gb3Cer (d18:1, C23:0) |
| 1156.78 | 1156.79 | 1156.76 | Gb3Cer (d18:1, C24:1) |
| 1158.78 | 1158.79 | 1158.77 | Gb3Cer (d18:1, C24:0) |
| 1249.73 | 1249.73 | 1249.69 | Gb4Cer (d18:1, C16:0) |
| 1277.71 | 1277.80 | 1277.67 | Gb4Cer (d18:1, C18:0) |
| 1331.80 | 1331.84 | 1331.94 | Gb4Cer (d18:1, C22:1) |
| 1333.86 | 1333.86 | 1333.95 | Gb4Cer (d18:1, C22:0) |
| 1359.85 | 1359.85 | 1359.95 | Gb4Cer (d18:1, C24:1) |
| 1361.85 | 1361.85 | 1361.99 | Gb4Cer (d18:1, C24:0) |
| 1249.77 | n.d. | n.d. | nLc4Cer (d18:1, C16:0) |
| 1359.90 | n.d. | n.d. | nLc4Cer (d18:1, C24:1) |
| 1361.90 | n.d. | n.d. | nLc4Cer (d18:1, C24:0) |
Minor protonated [M+H]+ ions detectable in the mass spectra are not listed in the table. Because Stx1 and Stx2 do not bind to Lc2Cer and nLc4Cer, these structures are not detected (n.d.) by both toxins. MS1 spectra of neutral GSLs with short-chain fatty acids (C14 to C18) are shown in Fig. 4 and those with long-chain fatty acids (C20 to C24) are displayed in supplementary Fig. I.