Table 2.
Summary of mass spectrometric detection of enterins predicted by the precursor
| AD | Predicted enterin | C# | [M+H]+calculated | [M+H]+ observed | % error | ppm |
|---|---|---|---|---|---|---|
| a | VSPKYGHNFVa | 1 | 1146.605 | 1146.607 | 0.00017 | 2 |
| b | GSPGFSHSFVa | 1 | 1020.490 | 1020.481 | 0.00088 | 9 |
| c | RLPSYGHSFLa | 1 | 1175.632 | 1175.625 | 0.00059 | 6 |
| d | AIPSYSHNFVa | 1 | 1133.574 | 1133.576 | 0.00017 | 2 |
| e | ADLGFTHSFVa | 1 | 1092.547 | 1092.53 | 0.00155 | 16 |
| f | AIPNFVHKFVa | 1 | 1170.678 | 1170.646 | 0.0027 | 27 |
| g | SSPFYGHNFVa | 1 | 1153.542 | 1153.557 | 0.0013 | 13 |
| h | VPGYSHSFVa | 8 | 991.500 | 991.479 | 0.0021 | 21 |
| i | IPGYSHSFVa | 1 | 1005.515 | 1005.489 | 0.00258 | 26 |
| j | TPGYSHSFVa | 3 | 993.479 | 993.473 | 0.0006 | 6 |
| k | APGYSHSFVa | 6 | 963.468 | 963.460 | 0.00083 | 8 |
| l | pELNFQHAFVa | 1 | 1085.533 | 1085.53 | 0.00028 | 3 |
| l′ | ELNFQHAFVa | 1 | 1103.563 | 1103.553 | 0.00091 | 9 |
| m | GQPGYGNAFLa | 1 | 1022.505 | 1022.501 | 0.00039 | 4 |
| n | pQPSYGHSFVa | 1 | 1003.460 | 1003.451 | 0.0009 | 9 |
| o | pQPGYSHSFVa | 1 | 1003.460 | 1003.451 | 0.0009 | 9 |
| p | VPSFGHSFVa | 1 | 975.505 | 975.498 | 0.0007 | 7 |
| q | pQPSYTHAFVa | 1 | 1031.491 | 1031.473 | 0.0017 | 17 |
| r | DPGFNHAFVa | 1 | 1002.479 | 1002.452 | 0.00269 | 27 |
| s | pQPSFGHSFVa | 2 | 987.465 | 987.468 | 0.0003 | 3 |
| t | pQPSFTHAFVa | 1 | 1015.496 | 1015.482 | 0.00138 | 14 |
| Average mass error: | 11 | |||||
The alphabetical designation (AD), amino acid sequence, and copy number (C#) on the precursor are shown for each of the enterins. Enterins that were biochemically identified are shown in bold (see also Table 1). The letter on the left of each peptide denotes their alphabetical designation in order of first appearance on the precursor as ENa through ENt (e.g., VSPKYGHNFVamide is Enterin A or ENa, etc.). The predicted mass ([M+H]+ calculated) and average mass observed (n = 10, [M+H]+ observed) in MALDI-TOF MS is shown for each, along with the % error in the measurement (also expressed as parts per million, ppm). Pyroglutamination of a number of enterins is based on MALDI-TOF analysis, not amino acid sequencing.