TABLE II.

Kinetic Analysis of Mutant Receptors

Mutant	k+1	k−1	K1	k+2	k−2	K2	β1	α1	Θ1	β2	α2	Θ2	k+b	k−b	KB
			μM			μM									mM
Wild type	126 ± 7	4500 ± 399	35	182 ± 11	14000 ± 525	77	262 ± 29	2310 ± 200	0.11	44600 ± 1010	1670 ± 33	27	24 ± 1	110000 ± 1940	4.6
αD89N	3 ± 0.1	1380 ± 52	460	37 ± 1	51800 ± 1420	1400	2070 ± 64	3200 ± 72	0.64	40000a	2500 ± 30	16	20 ± 1	97400 ± 1480	4.9
αD89E	14 ± 0.6	1160 ± 65	83	99 ± 3	33700 ± 744	340	962	3250	0.30	47500 ± 1620	2570 ± 63	18	21 ± 1	111000 ± 2500	5.3
αD89Tb	0.8 ± 0.03	910 ± 35	1140	44 ± 4	57000 ± 4680	1300	222 ± 23	3070 ± 323	0.07	49000 ± 6080	1380 ± 102	36	22 ± 1	107000 ± 2220	4.9
αT148L	114 ± 5	3600 ± 325	32	236 ± 11	16500 ± 626	70	249 ± 29	2450 ± 165	0.10	39400 ± 779	1680 ± 28	23	22 ± 1	109000 ± 1590	5.0
αT150A	334 ± 19	8480 ± 507	29	118 ± 3	26100 ± 778	221	287 ± 21	2220 ± 77	0.13	58000 ± 1860	2010 ± 52	29	20 ± 1	103000 ± 1860	5.2
αT148L + T150A	186 ± 18	2460 ± 252	13	105 ± 5	24400 ± 1080	232	ND	ND	–	39200 ± 1490	1270 ± 34	31	25 ± 1	101000 ± 1640	4.0
αT148D	28 ± 1	6060 ± 618	216	130 ± 10	27500 ± 1890	212	918 ± 116	2830 ± 162	0.32	31500 ± 1330	1500 ± 44	21	23 ± 1	99500 ± 1880	4.3
αD89N + T148D	89 ± 4	6530 ± 553	73	118 ± 5	29900 ± 1120	253	ND	ND	–	30100 ± 953	2320 ± 37	13	20 ± 1	109000 ± 2010	5.5
αT150D	50 ± 6	19500 ± 2550	390	89 ± 14	31500 ± 4850	354	232 ± 42	6870 ± 718	0.12	13900 ± 604	1730 ± 31	8	21 ± 2	122000 ± 4390	5.8
αD89N + T150D	59 ± 10	15300 ± 4650	259	82 ± 16	32100 ± 5120	391	249 ± 72	4980 ± 363	0.05	9580 ± 682	2060 ± 27	5	33 ± 3	138000 ± 4060	4.7

Kinetic parameters and error estimates are derived from global fitting of Scheme II to data obtained over a wide range of ACh concentrations (materials and methods). Units are μM⁻¹s⁻¹ for the association rate constants, s⁻¹ for all others. Gating equilibrium constants (Θ) are ratios of channel opening (β) to closing rate (α) constants. ND, a second open time component was not detectable.

^aOpening rate constant is a lower bound (see text and Fig. 6).

^bFitting was achieved using Scheme II modified to include two desensitized states linked to the open state. Fitted desensitization rate constants for αD89T, k_+d/k_−d, in units of s₋₁ are D₁ (41/529) and D₂ (65/30).