Brinkworth Craig S, Bowie John H
Department of Chemistry, The University of Adelaide, South Australia, 5005.
Rapid Commun Mass Spectrom. 2003;17(19):2215-25. doi: 10.1002/rcm.1172.
Collision-induced fragmentations of deprotonated maculatin 1 peptides provide significant sequencing information. When the peptide lacks those residues which can fragment through their alpha side chains (e.g. Thr, Ser, Glu and Gln in this study) the basic alpha and beta' backbone cleavages occur from the Mbond;H anion. When Thr, Ser, Glu and Gln are present, the ease of side-chain fragmentation of these residues is: Thr (loss of MeCHO) > Ser (CH(2)O) > Glu (H(2)O) > Gln (NH(3)). When one of more of these residues is (are) present, the alpha and beta' cleavages often occur from a fragment rather than the Mbond;H anion, e.g. for Thr, the (Mbond;H)(-)bond;MeCHO anion. These four residues also initiate gamma backbone cleavage reactions. The relative abundances of peaks resulting from gamma cleavage are Glu > Ser = Thr > Gln for maculatin 1 spectra. An unusual Gln19/Ile17 cyclisation/cleavage reaction occurs in maculatin spectra: the peptide Mbond;H anion must adopt a helical conformation in order for these two groups to interact. Analogous fragmentations have been reported previously in the negative ion spectra of the caerin 1 peptides.
去质子化的斑蛙肽1肽段的碰撞诱导碎裂提供了重要的测序信息。当肽段缺乏那些可通过其α侧链发生碎裂的残基时（例如本研究中的苏氨酸、丝氨酸、谷氨酸和谷氨酰胺），基本的α和β'主链裂解从[M-H]-阴离子发生。当存在苏氨酸、丝氨酸、谷氨酸和谷氨酰胺时，这些残基侧链碎裂的难易程度为：苏氨酸（失去乙醛）>丝氨酸（甲醛）>谷氨酸（水）>谷氨酰胺（氨）。当存在一个或多个这些残基时，α和β'裂解通常从一个片段而非[M-H]-阴离子发生，例如对于苏氨酸，是[(M-H)- -MeCHO]-阴离子。这四个残基还引发γ主链裂解反应。对于斑蛙肽1光谱，γ裂解产生的峰的相对丰度为谷氨酸>丝氨酸 = 苏氨酸>谷氨酰胺。在斑蛙肽光谱中发生了一种不寻常的谷氨酰胺19/异亮氨酸17环化/裂解反应：肽段[M-H]-阴离子必须采取螺旋构象，以便这两个基团相互作用。先前在caerin 1肽段的负离子光谱中已报道了类似的碎裂情况。
