FIGURE 6.

Cross-link formation between Cys substitutions in the center of the 1–2 loop and C-terminal end of the 3–4 loop. Membranes from the double Cys substitutions were treated with the reagents shown in each lane in the sequence indicated as described under “Experimental Procedures.” Following SDS-PAGE, Western blots were probed with anti-subunit a antibody. Cross-link formation led to increased electrophoretic mobility and a downward band shift as discussed in the text. A, V86C/L195C membranes; B, M93C/L195C membranes; C, V86C/T179C membranes; D, T179C/L195C membranes. βMSH, β-mercaptoethanol; O, no treatment.