Table 1: Matrix Assisted Laser Desorption-Ionization Mass Spectrometry (MALDI-MS) of ADP-PL-, IBMK-, VBMK-, NleBMK-, FBMK- and DEPC-Labeled Peptides of IleRS

Labeled Peptide Sequence Measured Mass Calculated Mass Mass Diff. Labeled Residue
ADP-PL-labeled peptides
601KMSK604 1055.1 493.6 561.5 K601
602MSKSIGNTVSPQDVMNK618 2398.7 1837.1 561.6 K604
IBMK-labeled peptides
451IESMVANRPDWCISR465 1904.9 1777.1 127.8 C462
717FCSVEMVSFYLDIIK731 1921.5 1794.2 127.3 C718
VBMK-labeled peptides
305FTHPFMG......DYVIGQK34 4574.5 4461.0 113.5 ?
325DAGTGA…PGHGPDDY342 1851.7 1738.7 113.0 H332/337
390GALLHVEK397 980.5 867.0 113.5 H394
451IESMVANRPDWCISR465 1890.6 1777.1 113.5 C462
468TWGVPMSLFVHK479 1515.5 1402.7 112.8 H478
717FCSVEMVSFYLDIIK731 1907.7 1794.2 113.5 C718
NleBMK-labeled peptides
390GALLHVEK397 993.6 867.0 126.6 H394
451IESMVANRPDWCISR465 1904.7 1777.1 127.6 C462
468TWGVPMSLFVHK479 1529.1 1402.7 126.4 H478
717FCSVEMVSFYLDIIK731 1921.8 1794.2 127.6 C718
FBMK-labeled peptides
390GALLHVEK397 1027.7 867.0 160.7 H394
468TWGVPMSLFVHK479 1563.5 1402.7 160.8 H478
717FCSVEMVSFYLDIIK731 1955.1 1794.2 160.9 C718
DEPC-labeled peptides
583APYRQVLTHG…KMSK604 2550.0 2477.8 72.2 H591
890VALS…CWHYTQDVGK912 2677.3 2605.0 72.3 H905

Masses, corresponding to [M + H]+ ions, are calculated (unlabeled peptides), or observed. Mass differences correspond to the covalent addition of one reagent (theoretical values are 561.1 for ADP-PL, 127.1 for L-isoleucine, 113.1 for L-valine, 127.1 for L-norleucine, 161.1 for L-phenylalanine and 72.0 Da for DEPC, cf Fig. 1).