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. Author manuscript; available in PMC: 2022 Aug 17.
Published in final edited form as: Chembiochem. 2021 Jul 8;22(16):2614–2618. doi: 10.1002/cbic.202100275

Figure 3.

Figure 3.

(A) Sequencing of the cyclo(X1PHPYX2X3GP) based on MS2 spectra. Note that three Pro residues in this octapeptide generate three different NPro-XaaC MS2 dipeptide product ions. Fragmentation strategies to query identities of X1 and X2 residues are illustrated. Annotation of (B) X1 and (C) X2 residues as Ile by the detection of the MS4 m/z 69 product ion. (D) Annotation of X3 as Ile by retention time comparison of the sponge detected PRMP against enzymatically synthesized cyclo(IPHPYILGP) and cyclo(IPHPYIIGP) standards.