Figure 10.
Allosteric model describing the Ca2+ activation of MthK. (A) Scheme I, in which eight Ca2+ bind to the channel, with each bound Ca2+ biasing the gating equilibrium toward the open states. (B) Po versus [Ca2+] relations predicted by Scheme IA (gray dashed lines) that incorporate H+ dependence with C = C0(KH/(KH+[H+])), as described in Results. Parameter values were: KH = 6.97 × 10−9 M H+; KC = 465 mM Ca2+; L = 3.2 × 10−4; C0 = 2,000. (C) Po versus [Ca2+] relations predicted by Scheme IB (blue dashed lines) that incorporate pH dependence with K = ([Ca2+]/KC)(KH/(KH+[H+])), as described in Results. Parameter values were: KH = 6.34 × 10−9 M H+; KC = 111 mM Ca2+; L = 3.2 × 10−4; C = 500. In B and C, symbols correspond to mean Po at each [Ca2+] at pH 9.0, 8.5, 8.1, 7.7, 7.3, 6.9, and 6.5 (as described in previous figures).