The limited trypsin digestion of rec-mTSPO: (A) The time course of the proteolytic cleavage of rec-mTSPO solubilized in DPC by trypsin. In the first minutes of trypsin digestion, two main fragments around 15 and 6.5 kDa were observed. The larger one disappeared over time, whereas shorter peptides below 6.5 kDa started to appear. After 48 h of digestion, only very short peptides around 2.6–3.7 kDa, probably corresponding to the transmembrane TM helices, were visible. (B) The effect of PK 11195 upon proteolytic cleavage: the time course in the presence of 100 µM PK 11195 (left panel) and the effect of increasing the concentration of PK 11195 with 3 min of trypsin digestion (right panel): The regions highlighted in red (in panel (A)) correspond to the fragment at 5 kDa that is not generated in the presence of PK 11195, whereas the fragments around 15 kDa (highlighted in red in left panel in (B)) remain. Moreover, only large fragments are observed in the presence of high concentrations of PK 11195 (red circle in right panel in (B)).