Table III. Kinetic constants of recombinant citrin, aralar1 and their C-terminal domains (CTDs) under de-energized conditions.

Carrier	External substrate	Internal substrate	Km (µM)	Vmax (µmol/min/g protein)	Turnover number (per min)	Expts (No.)
Citrin	aspartate	aspartate	56 ± 7	194 ± 28	14.9	6
	aspartate	glutamate	50 ± 7	172 ± 31	13.2	5
	glutamate	glutamate	228 ± 30	169 ± 26	13.0	3
	glutamate	aspartate	205 ± 22	185 ± 25	14.2	4
Citrin CTD	aspartate	aspartate	51 ± 5	350 ± 57	15.7	3
	aspartate	glutamate	47	369	16.5	2
	glutamate	glutamate	200	344	15.4	2
	glutamate	aspartate	182 ± 20	328 ± 50	14.7	3
Aralar1	aspartate	aspartate	51 ± 8	43 ± 6	3.2	5
	aspartate	glutamate	52 ± 9	52 ± 8	3.9	4
	glutamate	glutamate	220 ± 25	56 ± 9	4.2	4
	glutamate	aspartate	216 ± 25	49 ± 7	3.7	5
Aralar1 CTD	aspartate	aspartate	61	79	3.4	2
	aspartate	glutamate	55	96	4.1	2
	glutamate	glutamate	220	96	4.1	2
	glutamate	aspartate	229	88	3.8	2

The values were calculated from double reciprocal plots of the rate of [¹⁴C]aspartate or [¹⁴C]glutamate uptake versus substrate concentrations. The exchange was started by the addition of 20–800 µM [¹⁴C]aspartate or [¹⁴C]glutamate to proteoliposomes containing 20 mM aspartate or 20 mM glutamate and pre-incubated in the presence of valinomycin (1 µg/mg of phospholipids) and nigericin (50 ng/mg of phospholipids) in ethanol (10 µl/ml of liposomes) for 10 min. Transport was stopped after 30 s (citrin and its C-terminal domain) or 1 min (aralar1 and its CTD). The data represent means ± SE.