Figure 3: (A). Mass determination of the native Btae TX-I PLA2 by MALDI-TOF mass spectrometry. The MH+, MH2++ and 2MH+ species are shown in the mass spectrum. Insert MALDI-TOF mass spectrum, showing multiple alkylation channels of alkylated Btae TX-I. (B). ESI-QTOF-MS/MS spectrum of the tryptic peptides of 1504.5356 Da. Series of b and y ions, which are correspondent to the 11-residue-long tryptic peptide eluted in fraction 3 of the RPHPLC of the alkylated Btae TX-I containing the aspartic acid residue at position 49 in the amino acid sequence.