Figure 4
Quantitative analysis of Met oxidation of procaspase-3-D3A at different doses of Photofrin-PDT, as assessed using 15N-labeling. (a) Precursor peptides remaining after PDT with different doses of Photofrin. After LC-MS/MS analysis, the amounts of precursor peptides that remained for each detected peptide were calculated from the extracted ion chromatograms derived from the MSQuant results. The PDT versus control (14N/15N) ratios of precursor peptides derived from untreated samples (i.e., dosed with 0 μg/ml of Photofrin) were taken as 100%. (b) Oxidized peptide yields after PDT with different doses of Photofrin. The oxidized peptide yield for each detected peptide was determined from the extracted ion chromatograms as the proportion of oxidized peptide versus that of all possible forms of that particular peptide: oxidized peptide/(oxidized peptide+unmodified precursor peptide+peptides with other modifications). The oxidized peptide yield represented the summation of all kind of oxidations such as single and dual methionine oxidation, cystine trioxidation and so on (see ‘Supplementary Materials and Methods’). This calculation assumed that all possible modifications were identified
