17% SDS–PAGE gel showing the subtilisin treatment of BamC. Lane 1, pure BamC isolated after Ni–NTA affinity chromatography. Lanes 2–8, subtilisin treatment of BamC with increasing (from left to right) subtilisin:BamC ratios under standard conditions (277 K for 1 h followed by addition of PMSF). The subtilisin:BamC ratios were 1:10 000 (lane 2), 1:3000 (lane 3), 1:1000 (lane 4), 1:300 (lane 5), 1:100 (lane 6), 1:30 (lane 7) and 1:10 (lane 8). Lane M contains molecular-weight markers (kDa).