Figure 4.

Cooperative binding of MgADP and 8-azido-[γ-³²P]ATP. Membrane proteins from COS-7 cells expressing SUR1 were preincubated with 10 μM 8-azido-[γ-³²P]ATP. (A) After free 8-azido-[γ-³²P]ATP was removed, proteins were photoaffinity-labeled immediately (lane 1) or after incubation with 3 mM MgSO₄ for 15 min at 0°C (lane 2), with MgSO₄ for 15 min at 37°C (lane 3), with MgSO₄ and 1 mM ADP (lane 4), with MgSO₄ and 1 mM ATP (lane 5), or with MgSO₄ and 1 mM ATPγS (lane 6) for 15 min at 37°C as described for Fig. 1B (postincubation procedure). (B) Photoaffinity labeling is expressed as percentage of control (photoaffinity-labeled immediately) of those shown in A, lane 1.