TABLE 2.

Calculated K_i values for compounds that competed for l-Asp or l-Ala uptake in proteoliposomes

	l-Asp self-exchange		l-Ala self-exchange
	Ki	IC50	Ki	IC50
	mm		mm
l-Cysteine	2.0 ± 0.2	8.9	20 ± 2.7	65
l-Serine	NDa	ND	5.3 ± 1.7	28
l-CSA	0.59 ± 0.08	0.83	28 ± 0	28
l-CA	0.29 ± 0.05	0.47	14 ± 0	16
d-CA	0.14 ± 0.02	0.19	5.0 ± 0.2	9.0

^a ND, not determined. The K_i of serine for aspartate self-exchange was too high to measure, suggesting that serine is a specific inhibitor of l-alanine self-exchange but not l-aspartate self-exchange.