FIGURE 7.

Effects of mutations G93A and A4V on thiol/disulfide exchange reactions in hSOD1. Distribution of step sizes induced by the mechanical extension of I27₃-SOD-I27₃ in the presence of 2.5 mm TCEP for different protein preparations. Colors and nomenclature are the same as in Fig. 3. A, for mutant G93A, the intramolecular pathways A and B are less populated than for the wild-type protein (n = 96). B, the lack of reactivity of Cys-111 can be reproduced in wild-type hSOD1 by pre-incubation with the thiol alkylating agent maleimide (n = 69). C, for mutant A4V, the steps reporting on the reduction/isomerization of the disulfide bond are rare, suggesting that the disulfide bond in hSOD1 A4V is accessible to TCEP in solution (n = 111). D, similar results were obtained with apo hSOD1 (n = 51).