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TABLE I

Voltage-dependent Gating of K149 Mutants

Side chain at 149
Vo
z
Pmin
Volume
pKa
H-bond donors
n
 mV   3    
WT(K) −95 ± 1.1 0.90 ± 0.01 0.070 ± 0.008 167 10.4 25 
−56 ± 1.7 0.66 ± 0.02 0.017 ± 0.005 167   18 
−55 ± 2.1 0.71 ± 0.02 0.015 ± 0.005 194 ∼12 20 
−44 ± 0.7 0.84 ± 0.01 0.014 ± 0.004 90   13 
−43 ± 1.2 0.71 ± 0.02 0.009 ± 0.005 65   20 
−37 ± 1.0 0.82 ± 0.01 0.031 ± 0.007 95  45 
−33 ± 1.0 0.86 ± 0.01 0.014 ± 0.003 122  16 
−30 ± 1.1 0.84 ± 0.02 0.017 ± 0.006 103 9.1–9.5  13 
−24 ± 1.3 0.85 ± 0.02 0.028 ± 0.007 164   13 
N, Qa    125, 149   
D, Eb    117, 142 ∼4.5  
Wb    228   
Yb    197 9.6  
Side chain at 149
Vo
z
Pmin
Volume
pKa
H-bond donors
n
 mV   3    
WT(K) −95 ± 1.1 0.90 ± 0.01 0.070 ± 0.008 167 10.4 25 
−56 ± 1.7 0.66 ± 0.02 0.017 ± 0.005 167   18 
−55 ± 2.1 0.71 ± 0.02 0.015 ± 0.005 194 ∼12 20 
−44 ± 0.7 0.84 ± 0.01 0.014 ± 0.004 90   13 
−43 ± 1.2 0.71 ± 0.02 0.009 ± 0.005 65   20 
−37 ± 1.0 0.82 ± 0.01 0.031 ± 0.007 95  45 
−33 ± 1.0 0.86 ± 0.01 0.014 ± 0.003 122  16 
−30 ± 1.1 0.84 ± 0.02 0.017 ± 0.006 103 9.1–9.5  13 
−24 ± 1.3 0.85 ± 0.02 0.028 ± 0.007 164   13 
N, Qa    125, 149   
D, Eb    117, 142 ∼4.5  
Wb    228   
Yb    197 9.6  

Plots of apparent open probability (Po) versus voltage were fit as described in Materials and methods to derive the voltage at the midpoint in the voltage-activation curve (Vo), the apparent gating charge (z), and the minimum open probability (Pmin). The mean ± SEM is given for n patches. K149 mutants are listed in order of the severity of their effect along with the corresponding amino acid side-chain volume (V) (from Table 7 of Tsai et al, 1999), side-chain pKa, and number of side-chain hydrogen bond donors.

a

Mutants that expressed but had low current.

b

Mutants that did not give measurable current.

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