Figure 3.

Mass spectrometric identification of AruRGP A chain and B chain in extracts of A. rubens radial nerve cords. A: Predicted dimeric structure of AruRGP, showing the sequences of the A chain and B chain. The positions of disulfide bridges are shown with red lines and tryptic cleavage sites are marked with arrowheads. B,C: MS/MS data for the A chain and B chain, respectively, from reduced and alkylated samples of radial nerve extract without tryptic digestion. The b series of peptide fragment ions are shown in red, the y series in blue and additional identified peptide fragment ions in green. The amino acid sequence identified in the mass spectrum is highlighted at the top of the figures. C+57 represents cysteine modified by carbamidomethylation and M+16 represents oxidized methionine. The observed m/z of the precursor ion for the A chain (PETYVGMGSYCCLVGCTRDQLSQVC; B) is 980.75 with a charge state 3 + and an error of 0.41 ppm between the experimentally determined and predicted values (Mascot score = 57). The observed m/z of the precursor ion for the B chain (AEKYCDEDFHMAVYRTCTEH; C) is 860.02 with a charge state of 3 + and an error of 0.65 ppm between the experimentally determined and predicted values (Mascot score = 31). D,E: MS/MS data for the complete sequences of fragments of the A chain and B chains, respectively, derived from reduced and alkylated samples of radial nerve extract subjected to tryptic digestion, with annotations in the same format as in B and C. The observed m/z of the precursor ion for the A chain fragment (PETYVGMGSYCCLVGCTR; D) is 1055.44 with a charge state of 2 + and an error of –4.7 ppm between the experimentally determined and predicted values (Mascot score = 98). The observed m/z of the precursor ion for the B chain fragment (YCDEDFHMAVYR; E) is 541.22 with a charge state of 3 + and an error of –0.83 ppm between the experimentally determined value and predicted value (Mascot score = 45).