PHOSPHATIDYLSERINE BY TQ & MSQ ION-TRAP MASS SPEC WITH ELECTROSPRAY IONIZATION

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。各种分子种类的磷脂酰丝氨酸（PS）在负离子模式下以[M - H]-和[M - 2H + Alk]-的形式，以及在正离子模式下以[M + H]+、[M + Alk]+、[M - H + 2Alk]+和[M - 2H + 3Alk]+的形式（其中Alk = Li, Na）的低能CAD生成离子谱中含有丰富的片段离子，可用于结构测定。在CAD后，PS的[M - H]-离子发生解离，消除丝氨酸部分（C3H5NO2的损失），得到[M - H - 87]-离子，该离子相当于磷脂酸（PA）的[M - H]-离子，并产生ms3光谱，该光谱与PA的ms2光谱相同。PS的[M - 2H + Alk]-离子的主要碎裂过程是87的初始损失，生成[M - 2H + Alk - 87]-离子，然后是脂肪酸取代基作为酸（RxCO2H, x = 1,2）或作为碱盐（例如RxCO2Li， x = 1,2）的损失。这些断裂导致[M - 2H + Alk - 87 - R2CO2H]-比[M - 2H + Alk - 87 - R1CO2H]-丰度更高，[M - 2H + Alk - 87 - R2CO2Li]-比[M - 2H + Alk - 87 - R1CO2Li]-丰度更高；而[M - 2H + Alk - 87 - R2（或1）CO2Li]-离子的进一步解离使sn-1 （R1CO2-）上的羧酸阴离子比sn-2 （R2CO2-）上的羧酸阴离子优先形成。其他主要的断裂过程是由于脂肪酸取代基如烯酮的不同损失（Rx'CH=CO, x = 1,2的损失）。这使得[M - 2H + Alk - R2'CH=CO]-离子比[M - 2H + Alk - R1'CH=CO]？离子。在ms2光谱中，[M + H]+和[M + Alk]+离子的丰度较低，而在ms3光谱中丰度较高。[M + Alk]+离子的ms2谱包含一个独特的离子，可能是通过涉及重排步骤的破碎过程中磷酸基的内部损失。PS的[M - H + 2Alk]+离子生成主离子[M - H + 2Alk - 87]+，相当于PA单碱盐的碱加合离子，产生的[M - H + 2Alk - 87 - R1CO2H]+的丰度大于[M - H + 2Alk - 87 - R2CO2H]+。同样，PS的[M - 2H + 3Alk]+离子也产生了一个突出的[M - 2H + 3Alk - 87]+离子，该离子经历了连续的解离过程，涉及两个脂肪酸取代基的不同损失。由于上述串联质谱都包含几组离子对，这些离子对涉及到脂肪酸取代基作为烯酮或游离脂肪酸的不同损失，因此脂肪酸取代基的身份及其在甘油主链上的位置可以很容易地通过每对离子丰度的巨大差异来确定。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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 + 2Alk]+, and [M - 2H + 3Alk]+ (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 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 - 87]- 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 - R2(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 Rx'CH=CO, x = 1,2). This results in a more prominent [M - 2H + Alk - R2'CH=CO]- ion than [M - 2H + Alk - R1'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 + 2Alk]+ ion of PS yields a major [M - H + 2Alk - 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 + 2Alk - 87 - R1CO2H]+ than [M - H + 2Alk - 87 - R2CO2H]+. Similarly, the [M - 2H + 3Alk]+ ion of PS also yields a prominent [M - 2H + 3Alk - 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.