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. 2013 Nov 4;110(47):E4557–E4566. doi: 10.1073/pnas.1319218110

Table 2.

Na+ affinity of hSGLT1 mutants

Kd, mM KdA, mM KdB, mM k16/k61 τo, ms k16, s−1 k61, s−1
hSGLT1 20 33* 10* 100 <2 530 5
Near sugar binding site
 H83C 120 >150 6 6 170 10
 T287C 20 200
 Y290C 57 30 110 2.4 9 80 33
 Y290S 57 30 110 1.4 17 60 25
 Y290F 120 30 >150 24 10 100 4
 W291C 55 30 110 2 16 21 43
 W291F 20 100 4 275 3
 Q457C 20 250 2 530 2
Near Na2 site
 D204E >150 2.6
 S392A 122 50 >150 10 19 48 5
Other
 F101C 18 35
 F453C 20 33* 10* 125
 G507C 20 33* 10* 100

Na+ affinities, Kd (= √(k21/k12)) for the three-state and KdA (= kN1/k1N) and KdB (= k2N/kN2) for the four-state model (Fig. 1), were estimated from the V0.5 vs. log [Na+]o data (Figs. 5 and 6). Parameters are those obtained in individual cells, but representative of three to five experiments conducted on different batches of oocytes. For all proteins, the variation in Kd was 10% and, excluding the WT group, the variation in KdA was 10%. τo was obtained from the time constants for relaxation of the transient charge movements in the absence of sodium (e.g., Fig. 7). The values given for KdA and KdB are for those where V0.5 in the absence of Na+ fell within the experimental range (Table 1), reducing the number of unknown parameters in Eq. 9. For all proteins, the number of Na+ ions (n) was 2, and net charge (z) was 1. z1 = 0.7, z2 = 0.3, for the three-state model and z1 = 0.7, z2 = 0.15, z3 = 0.15 for the four-state model. The absence of data for mutants (—) reflects those where V0.5 in the absence of Na+ fell outside the experimental range (Table 1) and those not determined.

*

The Na+ affinities of the two sites for the WT group are similar, because the three-state model fitted the data, and Kd = √KdAKdB.

Loo et al. (24).