FIGURE 5.

High concentrations of protein crowders restore wild-type ferritin ion channel function disrupted by substitutions of conserved, channel amino acids. Fe²⁺ exit (Fe²⁺-bipyridyl complex formation), a process dependent on the surface-limited reduction and dissolution of caged ferritin minerals, was measured in the presence and absence of high concentrations of unrelated protein, BSA (3.8 mm) or lysozyme (8.7 mm), that mimic the crowded cytoplasm. The percentage free volume excluded (40) was 17% for lysozyme and 37% for BSA. Fe²⁺ exit was triggered with NADH and FMN and monitored as Fe²⁺-(bipyridyl)₃ outside the cage (11, 12). The mean and S.D. (error bars) from 5–8 independent experiments with two different protein preparations are shown. *, significantly different (p < 0.0001) from wild-type ferritin.