Table 1.

Kinetic constants of recombinant AtUCP1 and AtUCP2

The values were calculated from linear regression of double reciprocal plots of the initial rates of the indicated homo-exchanges versus the external substrate concentration. The exchanges were started by adding appropriate concentrations of labeled substrate to proteoliposomes preloaded internally with the same substrate (10 mm). The reaction time was 7 and 20 s for AtUCP1 and AtUCP2, respectively. The values are means ± S.E. of at least three independent experiments carried out in duplicate.

Carrier and substrate	Km	Vmax
	mm	mmol/min × g protein
AtUCP1
[14C]Aspartate/aspartate	0.8 ± 0.1	30 ± 6
[14C]Glutamate/glutamate	1.9 ± 0.2	24 ± 6
[14C]Malate/malate	2.0 ± 0.2	33 ± 6
AtUCP2
[14C]Aspartate/aspartate	0.8 ± 0.1	4.5 ± 0.5
[14C]Glutamate/glutamate	2.5 ± 0.2	4.2 ± 0.4
[14C]Malate/malate	2.4 ± 0.1	4.3 ± 0.4