Figure 6.

Disulfide cross-linking of mutants (A) [H H L] and (B) [L H H]. Oxidation of dicysteine mutants by atmospheric oxygen was catalyzed by 15 μM Cu²⁺ ions for the indicated time before quenching. The dicysteine mutant [H H L] has only 11 residues between the two cysteines, resulting in an unobservable difference in mobility on SDS gels (data not shown). This mutant was thus analyzed by isoelectric focusing (A). The disulfide form runs further from the anode, which is at the bottom of the gel as shown. The mutant [L H H] was analyzed on 20% homogeneous Phast gels (B), where the disulfide form has slightly greater electrophoretic mobility.