Fig. 6. Trypsin digestion of SphB1 at the cell surface. BPSM (WT, lanes 1–4 and 8–10) and BPLC5 (ΔsphB1, lanes 5–7 and 11–13) cells were treated with trypsin with (lanes 8–13) or without (lanes 2–7) a prior Tris–EDTA treatment to permeabilize the outer membrane. In lane 1, BPSM cells were mock treated for 1 h. At the indicated times, aliquots were withdrawn and trypsin was inactivated with AEBSF. The proteins were precipitated and analysed by immunoblotting with the anti-SphB1 antiserum. The masses in kDa of the molecular markers are indicated at the left.