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. 2021 Mar 2;12:636597. doi: 10.3389/fpls.2021.636597

FIGURE 3.

FIGURE 3

Activity of recombinant Nb-P4Hs on different synthetic peptide substrates. (A) Representative ESI-LC-MS spectra of doubly charged ions [(M + 2H)2+] of the IgA1 peptide (VTVPVPSTPPTPSPSTPPTPSPS), (B) double charged ions of the EPO peptide (AQKEAISPPDAASAA), (C) triple charged ions [(M + 3H)3+] of the STRUBBELIG peptide (DGTPFNTSIITPPPPPCCDPPPATHR), (D) double charged ions of the Art v 1 peptide (AAGGSPSPPADGGSPPPPADG). Proline hydroxylation can be observed by the mass increments of 16 Da in single charged ions (or 8 and 5.3 Da in double and triple charged ions, respectively). The isotopic pattern is correct for each peptide except for Art v 1 where an undesired ammonium adduct (+17 Da) adds to the intensity of the second isotopic peak. In this case the height of the first isotopic peak should be accepted.