Fig. 3. Conformational stability of mutant serpins. (A) 7.5-15.0% (w/v) non-denaturing PAGE of cell extracts from flies carrying the E421K (nec⁹) mutation show reduced levels of native-like protein, N, and an increase in levels of higher molecular mass species, H. The more extreme phenotype of nec¹ is associated with a further reduction in native protein. (B) 7.5% (w/v) TUG PAGE demonstrates that the higher molecular mass species (arrows) observed in both nec⁹ and nec¹ are insensitive to denaturation in 8M urea. This behavior is characteristic of loop-sheet polymers such as those observed in the livers of individuals with Z-₁-antitrypsin deficiency. These stabilized polymers are not observed in the wild-type flies. (C) The profile of monomeric ₁-antitrypsin and polymerized Z-₁-antitrypsin are shown for comparison, using purified proteins stained with Coomassie. The left of each gel represents 0 M urea and the right 8 M urea.