FIGURE 3.

SURs have reduced affinity for ATPγS versus ATP. A, comparison of MgATPγS versus MgATP effects. The curves are best fits to a four-state model (Fig. 1B, inset). The best-fit dissociation constants are K_T = 1 and 29 μm for MgATP and MgATPγS, respectively. The β values are 40 and 11.6 for MgATP and MgATPγS, respectively. The dissociation constant, K_G = 0.63 nm for GBC, was determined independently. B, comparison of the affinities of SUR1_E1507Q for ATP⁴⁻ versus ATPγS⁴⁻. The solid curves are the best fits to the four-state model; the parameters are K_T = 94 versus 234 μm; β = 40 versus 3.2, ATP⁴⁻ versus ATPγS⁴⁻, respectively. The dissociation constant for GBC, K_G = 0.63 nm, was fixed during fitting.