Fig. 3
MS/MS spectra of lipids acquired in negative mode showing differences between wt and hyh mice. a PS (42:9) (m/z 856.5) spectrum. Fragments 1 and 2 correspond to the carboxylated 20:3 and 22:6 chains, respectively. Ions 3 and 4 correspond to neutral loss of 22:6 as a ketene and serine and to neutral loss of 20:3 as RCOOH and serine, respectively. Fragment 5 represents the loss of serine from [M-H]-. The spectrum also shows the fragmentation pattern of the more abundant PI (36:4) (m/z 857.5). b PI (38:5) (m/z 883.5) spectrum. Fragments shared with the more abundant PI (38:4): 1, 2, 3, 4 (different forms of inositol phosphate ions) and 6 (carboxylated 20:4 chain). Ion 5 is the carboxylated 18:1 chain. Ion 7 represents the neutral loss of the 20:4 RCOOH group and inositol from [M-H]-. Ion 8 represents the neutral loss of the 18:1 chain and inositol and/or the neutral loss of 18:0 and inositol from PI (38:4). Fragments 9 and 10 represent the neutral loss of 20:4 and 18:1 as RCOOH groups, respectively. c PI (38:4) (m/z 885.5) spectrum. Fragments 1, 2, 3, and 4 correspond to inositol phosphate (IP)–2H2O, IP –H2O, IP, and IP + glycerol backbone ions, respectively. Ions 5 and 6 are the carboxylated 18:0 and 20:4 chains, respectively. Fragments 7 and 8 represent the neutral loss of 20:4 and 18:0 RCOOH groups and inositol from [M-H]-, respectively. Ions 9 to 12 correspond to the neutral loss of 20:4 and 18:0 either as RCOOH or as ketenes, respectively. The m/z 885 peak is the precursor ion [M-H]-