Studies on phosphatidylserine by tandem quadrupole and multiple stage quadrupole ion-trap mass spectrometry with electrospray ionization: Structural characterization and the fragmentation processes
Studies on phosphatidylserine by tandem quadrupole and multiple stage quadrupole ion-trap mass spectrometry with electrospray ionization: Structural characterization and the fragmentation processes
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DOI：
10.1016/j.jasms.2005.04.018
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发表时间：
2005-09-01
影响因子：
3.2
通讯作者：
Turk, J
中科院分区：
文献类型：
--
作者：
Hsu, FF;Turk, J
以[M-H](-)和[M-2H+ALK](-)形式存在的各种磷脂酰丝氨酸(PS)分子在负离子模式下以及以[M+H](+)、[M+ALK](+)、[M-H+2AIk](+)和[M-2H+3AIk](+)形式存在的低能CAD乘积离子谱中含有丰富的碎片离子，可用于结构测定。在CAD后，PS的[M-H]-离子发生解离以消除丝氨酸部分(失去C3H5NO2)，得到一个[M-H-87]-离子，它相当于磷脂酸(PA)的[M-H]离子2，并产生与PA的MS2-谱相同的MS3-谱。PS的[M-2H+ALK]-离子的主要碎裂过程是由87的初级损失产生[M-2H+ALK-871离子，然后以酸(RxCO2H，x=1，2)或碱性盐(例如，RxCO2Li，x=1，2)的形式损失脂肪酸取代基。这些碎裂导致[M-2H+ALK-87-R2CO2H](-)比[M-2H+ALK-87-R1CO2H](-)丰度高，[M-2H+ALK-87-R2CO2Li](-)比[M-2H+ALK-87-R1CO2Li](-)丰度高；当[M-2H+alk-87-R-2((或1))Co2Li](-)离子进一步解离时，sn-1(R1CO2-)处的羧酸阴离子优先于sn-2(R2CO2)(-)处的羧酸阴离子的形成，而另一个主要的裂解过程是由于脂肪酸取代基作为酮类的不同损失(R-x‘ch=CO，x=1，2)。这导致了比[M-2H+ALK R，‘CH=CO](-)离子更显著的[M-2H+ALK-R2’CH=CO](-)离子。在[M+H](+)和[M+ALK](+)离子的MS2谱中，[M+H](+)和[M+AlK](+)离子的MS2谱中丰度较低，但在MS3谱中丰度较高。[M+ALK](+)离子的MS2光谱包含一个独特的离子，可能通过涉及重排步骤的碎裂过程，对应于磷酸基团的内部损失。PS的[M-H+2AIk](+)离子产生一个主要的[NI-H+2AIk-87]离子，相当于PA一碱盐的碱加合离子，并产生比[M-H+2AIk-87R2Co2H](+)+更丰富的[M-H+2AIk-87-R1Co2H](+)+。类似地，PS的[M-2H+3Alk](+)离子也产生显著的[M-2H+3Alk-87](+)离子，它经历了连续的解离过程，涉及两个脂肪酰基取代基的不同损失。由于所有上述串联质谱图都包含几组离子对，涉及脂肪酸取代基作为酮或作为游离脂肪酸的不同损失，因此通过每对离子丰度的巨大差异可以很容易地确定脂肪酰基取代基及其在甘油主链上的位置。(C)2005年美国质谱学学会。
Low-energy CAD product-ion spectra of various molecular species of phosphatidylserine (PS) in the forms of[M-H](-) and [M-2H + Alk](-) in the negative-ion mode, as well as in the forms of [M + H](+), [M + Alk](+), [M-H + 2AIk](+), and [M-2H + 3AIk](+) (where Alk = Li, Na) in the positive-ion mode contain rich fragment ions that are applicable for structural determination. Following CAD, the [M - H] - ion of PS undergoes dissociation to eliminate the serine moiety (loss of C3H5NO2) to give a [M-H-87]-ion, which equals to the [M - H]ion 2 of a phoshatidic acid (PA) and give rise to a MS3-spectrum that is identical to the MS2-spectrum of PA. The major fragmentation process for the [M-2H + Alk]- ion of PS arises from primary loss of 87 to give rise to a [M - 2H + Alk - 871 ion, followed by loss of fatty acid substituents as acids (RxCO2H, x = 1,2) or as alkali salts (e.g., RxCO2Li, x = 1,2). These fragmentations result in a greater abundance of [M-2H + Alk-87-R2CO2H](-) than [M-2H + Alk-87-R1CO2H](-) and a greater abundance of [M-2H + Alk-87 R2CO2Li](-) than [M-2H + Alk-87-R1CO2Li](-); while further dissociation of the [M - 2H + Alk-87-R-2((or 1))Co2Li](-) ions gives a preferential formation of the carboxylate anion at sn-1 (R1CO2-) over that at sn-2 (R2CO2)(-) Other major fragmentation process arises from differential loss of the fatty acid substituents as ketenes (loss of R-x'CH=CO, x = 1,2). This results in a more prominent [M-2H + Alk - R2'CH=CO](-) ion than [M-2H + Alk R,'CH=CO](-) ion. Ions informative for structural characterization of PS are of low abundance in the MS2-spectra of both the [M + H](+) and the [M + Alk](+) ions, but are abundant in the MS3-spectra. The MS2-spectrum of the [M + Alk](+) ion contains a unique ion corresponding to internal loss of a phosphate group probably via the fragmentation processes involving rearrangement steps. The [M-H + 2AIk](+) ion of PS yields a major [NI - H + 2AIk - 87] ion, which is equivalent to an alkali adduct ion of a monoalkali salt of PA and gives rise to a greater abundance of [M-H + 2AIk-87-R1Co2H](+) than [M-H + 2AIk-87 R2Co2H](+) +. Similarly, the [M-2H + 3Alk] (+) ion of PS also yields a prominent [M - 2H + 3AIk - 87] (+) ion, which undergoes consecutive dissociation processes that involve differential losses of the two fatty acyl substituents. Because all of the above tandem mass spectra contain several sets of ion pairs involving differential losses of the fatty acid substituents as ketenes or as free fatty acids, the identities of the fatty acyl substituents and their positions on the glycerol backbone can be easily assigned by the drastic differences in the abundances of the ions in each pair. (c) 2005 American Society for Mass Spectrometry.