Figure 6. SDS–PAGE analysis and fluorescence determination to examine binding of FFCK to untruncated βA3-crystallin and its two major truncated products. Lanes 4 and 5 represents βA3-crystallin truncated species, which were recovered following treatment of βA3-crystallin with CHAPS, and were labeled with FFCK. The lanes 6 and 7 represented βA3-crystallin treated with CHAPS but complete degradation of intact crystallin to 22 and 27 kDa species was not allowed to determine if all three species (intact, 22, and 27 kDa species) show labeling with FFCK. The untruncated βA3-crystallin (Coomassie blue stained in lane 7 of A) and its two truncated species of 22 and 27 kDa (Coomassie blue-stained bands in lane 4 and 7 in A) showed binding to FFCK (25 μM, final concentration) as represented by fluorescent bands (lane 4 and 7 in B). The results suggest that because of FFCK binding, the protease active site is present in both untruncated βA3-crystallin and its major truncated species II and III.