TABLE 2.

Effect of externally added anions on the [¹⁴C]citrate/citrate exchange catalyzed by reconstituted single-Cys site 2 CTP variants

Reconstituted site 2 single-Cys CTP variants were incubated with 1–2 mm [¹⁴C]citrate plus a 25-fold excess of potential competing anion. Controls contained water in place of competing anion. Data are presented as mean percentage inhibition ± S.E. from 3 to 6 experiments. Transport reactions and data calculations were conducted as described under “Experimental Procedures.” Statistical differences among the Cys-less and the site 2 CTP variants with a given anion were evaluated with the one-way analysis of variance test. Only with pyruvate were no statistical differences found. Significance was then determined with the Bonferroni multiple comparisons post hoc test. α-KG is α-ketoglutarate; PEP is phosphoenolpyruvate.

CTP variant	Isocitrate	α-KG	Malate	Succinate	Malonate	PEP	ADP	Phosphate	Pyruvate	Glutamate
Cys-less	60 ± 1	20 ± 2	16 ± 2	18 ± 1	20 ± 6	34 ± 1	17 ± 5	9 ± 2	1 ± 3	−7 ± 9
K37C	7 ± 1a	−1 ± 2b	6 ± 1	2 ± 3	7 ± 4	7 ± 2a	12 ± 5	9 ± 4	3 ± 6	−4 ± 5
R181C	15 ± 2a	34 ± 1	38 ± 4a	37 ± 7b	35 ± 3	27 ± 5	11 ± 3	34 ± 5c	6 ± 7	−8 ± 8
K239C	14 ± 2a	4 ± 6	13 ± 3	−2 ± 4b	11 ± 5	19 ± 3	6 ± 8	17 ± 5	14 ± 4	−4 ± 5
R276C	51 ± 5	42 ± 3b	45 ± 2a	45 ± 1c	35 ± 2	69 ± 7a	55 ± 2c	35 ± 3c	5 ± 4	39 ± 5a
R279C	47 ± 5b	64 ± 9a	52 ± 3a	48 ± 1c	57 ± 6a	64 ± 8c	44 ± 8b	54 ± 7a	7 ± 3	32 ± 2c

^a p < 0.001 versus Cys-less.

^b p < 0.05 versus Cys-less.

^c p < 0.01 versus Cys-less.