Fig. 2. Analysis of the protein–protein interaction using co-immunoprecipitation. Cytosolic (a) and microsomal fractions (b) were incubated with an anti-PtIGS antibody bound to the AminoLink Plus Coupling Resin. After elution with an acidic buffer, proteins were separated by SDS-PAGE using a 12.5% acrylamide gel for (a) and 10% for (b). After the samples corresponding to (a) 0.205 and (b) 0.057 g wet weight leaves were analyzed, total proteins were visualized with silver staining. As the control, PtIGS in the samples corresponding to 0.041 and 0.057 g wet weight leaves was also detected with western blotting using the anti-PtIGS antibody. C1–C6 and M1–M10 show the regions that were cut from gels and subjected to MS/MS analysis. The symbols "+" and "-" represent the use of AminoLink Plus Coupling Resins bound with anti-PtIGS antibody and without antibody, respectively.