Electrophoretic profile of TAPBb upon preincubation at different temperatures. Purified protein was incubated at 37 (lane 1), 50 (lane 2), 60 (lane 3), 70 (lane 4), or 100°C (lane 5) for 10 min in the reaction buffer, following by SDS-8% PAGE analysis under nonreducing conditions. The gel was silver stained. Oligomeric (*) and monomeric (**) states of TAPBb are indicated.