Table 1.

Electrogenic Activity of Mutant Constructs

cRNA	I p	cRNA	I p
	nA		nA
WT	−78.7 ± 10.4	A393C	−33.3 ± 5.8
N140C	0	S418C	0
S166C	0	S434C	0
S190C	0	A460C	−41.3 ± 7.4
L234C	0	A513C	0
A239C	0	S532C	−34.7 ± 3.5
S318C	−26.4 ± 5.2	A538C	−41.3 ± 5.8
S373C	−25.3 ± 4.8	S583C	0

Cotransport activity of mutants expressed in Xenopus oocytes, assayed as the current induced by 1 mM P_i (I _p) in 100 mM Na⁺, pH 7.4, with the cell voltage clamped to −50 mV. I _p values are mean ± SEM (n = 5). Wild-type response is for oocytes from the same donor frog used to express the mutant protein. All mutants that showed expression were exposed to 100 μM MTSEA (2 min) and the response to P_i was retested. Only the response of mutant S460C was suppressed by this procedure.