Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.6 (CAD)
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We report negative-ion electrospray tandem mass spectrometric methods for structural characterization of cardiolipin (CL), a four-acyl-chain phospholipid containing two distinct phosphatidyl moieties, of which structural assignment of the fatty acid residues attached to the glycerol backbones performed by low-energy CAD tandem mass spectrometry has not been previously described. The low-energy MS2-spectra of the [M - H]- and [M - 2H]2- ions obtained with ion-trap or with tandem quadrupole instrument combined with ion-trap MS3-spectra or with source CAD product-ion spectra provide complete structural information for CL characterization. The MS2-spectra of the [M - H]- ions contain two sets of prominent fragment ions that comprise a phosphatidic acid, a dehydrated phosphatidylglycerol, and a (phosphatidic acid + 136) anion. The substantial differences in the abundances of the two distinct phosphatidic anions observed in the MS2-spectra of the [M -H]- ions lead to the assignment of the phosphatidyl moieties attached to the 1' or 3' position of central glycerol. Upon further collisional dissociation, the MS3-spectra of the phosphatidic anions provide information to identify the fatty acyl substituents and their position in the glycerol backbone. The MS2-spectra of the [M - 2H]2- ions obtained with TSQ or ITMS contain complementary information to confirm structural assignment. The applications of the above methods in the differentiation of cardiolipin isomers and in the identification of complex cardiolipin species consisting of multiple molecular structures are also demonstrated.
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PMID:Structural characterization of cardiolipin by tandem quadrupole and multiple-stage quadrupole ion-trap mass spectrometry with electrospray ionization. 1579 18

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.
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PMID:Studies on phosphatidylserine by tandem quadrupole and multiple stage quadrupole ion-trap mass spectrometry with electrospray ionization: structural characterization and the fragmentation processes. 1602 63