Dass C, Mahalakshmi P
Department of Chemistry, University of Memphis, TN 38152, USA.
Rapid Commun Mass Spectrom. 1995;9(12):1148-54. doi: 10.1002/rcm.1290091213.
Liquid secondary ionization mass spectrometry (LSIMS) operating in the positive- and negative-ion modes was used to study fragmentation profiles and to obtain the amino acid sequences of a set of seven phosphoenkephalin peptides. The use of glycerol as the liquid matrix led to increase in fragmentation of phosphopeptides. The prominent amino acid sequence-determining ions in the positive-ion mode are y-type C-terminal ions; the N-terminal sequence-specific ions are observed sporadically. The most dominant ions in those mass spectra, however, are the immonium ions and a few low-mass side-chain cleavage products. The mass spectra in the negative-ion mode are more information-rich, and provide data complementary to that from the positive-ion mode. The phosphate group marker ions, m/z 79 (PO-3) and 97 (H2PO-4), are prominent and both N- and C-termini sequence ions are formed with equal facility in this mode of analysis. Both positive- and negative-ion mass spectral data are useful in determining the amino acid sequence of all the seven phosphoenkephalins. Thus, LSIMS alone can be a viable option to the tandem mass spectrometry approach when sufficient quantities (> 50 nmol) of phosphopeptides are available.
采用正离子和负离子模式运行的液体二次离子质谱法（LSIMS）来研究一组七条磷酸脑啡肽肽段的裂解图谱并获取其氨基酸序列。使用甘油作为液体基质会导致磷酸肽裂解增加。正离子模式下突出的氨基酸序列测定离子是y型C端离子；N端序列特异性离子偶尔可见。然而，这些质谱中最主要的离子是亚铵离子和一些低质量的侧链裂解产物。负离子模式下的质谱信息更丰富，并提供与正离子模式互补的数据。磷酸基团标记离子m/z 79（PO-3）和97（H2PO-4）很突出，并且在这种分析模式下N端和C端序列离子的形成难易程度相同。正离子和负离子质谱数据在确定所有七条磷酸脑啡肽的氨基酸序列方面都很有用。因此，当有足够量（>50 nmol）的磷酸肽可用时，仅LSIMS就可以成为串联质谱法的一个可行选择。
