TABLE 2.

Orientation of substrate binding site determines aspartate K_0.5

Treatment of A364C-Glt_Ph in liposomes with thiol-modifying agents allows determination of sided kinetics of transport. Shown are the initial rate of l-[³H]aspartate transport as a function of [l-[³H]aspartate] in the outside buffer in the presence of saturating Na⁺ concentrations and the initial rate of l-[³H]aspartate transport as a function of [Na⁺] in the outside buffer in the presence of saturating l-[³H]aspartate concentrations. Kinetic parameters for Glt_Ph were derived by fitting the l-aspartate concentration-response data to the Michaelis-Menten equation and fitting the Na⁺ concentration-response data to the Hill equation. The values are averaged from experiments performed in triplicate, and errors indicate S.E.

	ISO	RSO
Aspartate K0.5 (nm)	140.7 ± 26.2	39.3 ± 6.7
Na+ K0.5 (mm)	2.1 ± 0.3	2.2 ± 0.2