. 2014 Mar 18;106(6):1268–1279. doi: 10.1016/j.bpj.2014.01.043

Table 1.

Functional properties of mutants

Repeat unit	Construct	³²P uptake	Presteady-state	Activation index^a
Repeat unit	Construct	³²P uptake	100Na	P_i^a	Na^a
	WT	+	+	0.61	0.63
RU1	S164A	−	+	n.a.	n.a.
	S164C	−	+	n.a.	n.a.
	T195C	−	+	n.a.	n.a.
	S196C	−	−	n.a.	n.a.
	N199C^b	+	n.d.	0.10	0.03
	R210C	+	+	0.60	0.65
RU2	Q417C	+	+	0.46	0.39
	S418C	−	+	n.a.	n.a.
	S419A	−	+	n.a.	n.a.
	S419C	−	+	n.a.	n.a.

n.a.: not applicable; n.d.: not determined; −: not detected; +: detected.

Presteady-state relaxations suppressed (−) or left unchanged (+) by 1 mM P_i.

Bold entries indicate constructs used for immunohistological confirmation of membrane expression (Fig S6).

Activation indices were defined as follows: the P_i index was the ratio of P_i-induced current with 0.1 mM P_i to that with 1 mM P_i in 100 mM Na⁺ and the Na⁺ index was the ratio of the response to 1 mM P_i with 50 mM Na⁺ to that with 100 mM Na⁺. Both indices were determined at −50 mV. These ratios give an approximate indication of shifts in the apparent substrate affinity for screening purposes (e.g., (56)).

From (52) for rat NaPi-IIa isoform, equivalent to N199 in human NaPi-IIa.