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TABLE I

Comparison of Kinetic Parameters for Mutant and Wild-Type Transporters (Glutamate as Substrate)


Kma for Glu
Imaxb (exchange)
Km for Na+, glutamate freec
Km for Na+, glutamate boundd
τslowe
 μM pA mM mM ms 
E373Q 10 ± 5 −240 ± 20 80 ± 40 7 ± 1 <50 
D439N 500 ± 350 −28 ± 7 110 ± 40 100 2600 ± 100 
D454N 20 ± 4 −560 ± 60 90 ± 20 7 ± 2 <50 
WT 1.4 ± 1 −510 ± 120 120 ± 20 8 ± 1 <50 

Kma for Glu
Imaxb (exchange)
Km for Na+, glutamate freec
Km for Na+, glutamate boundd
τslowe
 μM pA mM mM ms 
E373Q 10 ± 5 −240 ± 20 80 ± 40 7 ± 1 <50 
D439N 500 ± 350 −28 ± 7 110 ± 40 100 2600 ± 100 
D454N 20 ± 4 −560 ± 60 90 ± 20 7 ± 2 <50 
WT 1.4 ± 1 −510 ± 120 120 ± 20 8 ± 1 <50 
a

Apparent affinity for glutamate in the homoexchange mode.

b

Imax was determined at saturating glutamate concentrations in the homoexchange mode.

c

Apparent affinity of Na+ to glutamate-free transporter.

d

Apparent affinity of Na+ to glutamate-bound transporter.

e

Time constant of rising phase of the inward current induced by glutamate in the forward transport mode (D439N) or exchange mode (E373Q, D454N, and WT).

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