FIG. 4.

Native PAGE analysis of pronase-treated Triton X-100 extracts from BBMs containing ¹²⁵I-CPE bound at 4°C. ¹²⁵I-CPE was bound to BBMs at 4°C in the absence (− lanes) or the presence (+ lanes) of a 50-fold excess of unlabeled CPE. After the unbound ¹²⁵I-CPE was removed, BBMs were extracted with cold DPBS containing 1% Triton X-100 and then treated at 4°C with pronase (300 μg) for 5 min (third and fourth lanes) or 1 h (fifth and sixth lanes); the first and second lanes contain samples that were not pronase treated. After the conclusion of pronase treatment, protease inhibitors were added (see Materials and Methods) and all samples were electrophoresed on a native 6% polyacrylamide gel. The migration of small complex is noted at the left. The gel shown is representative of gels used in six independent repetitions of the experiment.