TABLE 2.

Affinities of E2P for lumenal Ca²⁺ estimated by kinetic analyses and those determined at steady-state analyses As described in Fig. 8B, the lumenal Ca²⁺ affinities (K_0.5) of E2P of the wild type and the mutant Y122A were estimated by the kinetic analyses of the lumenal Ca²⁺-induced E2P to E1PCa₂ reverse transition and of the forward E1PCa₂ to E2P transition. The K_0.5 values and the Hill coefficients (n_H) thus estimated kinetically in Fig. 8 in the absence and presence of 0.1 m K⁺ at pH 7.3 are summarized here. Listed together are those determined by the steady-state analyses of the lumenal Ca²⁺-induced change in the accumulated fraction of the ADP-insensitive EP (E2P) under otherwise the same conditions in Figs. 2 and 6 for the mutant Y122A with and without K⁺ and the wild type without K⁺.

	K+ (0.1 m)	Estimated by kinetic analyses		Determined by steady-state analyses
		K0.5	nH	K0.5	nH
		mm		mm
WT	+	1.48	2.2	–a	–a
	–	0.45	1.7	0.40	1.5
Y122A	+	0.15	1.9	0.16	1.9
	–	0.22	1.7	0.22	2.2

^aNot determined because the accumulation of ADP-insensitive EP was very low at all the Ca²⁺ concentrations examined, and therefore possible change was not revealed