Table 1. Effects of Mg²⁺ and P_i on ATP transport.

Influx (a) and efflux (b) of ³H-labelled ATP were assayed for 5 and 10 min in the presence or absence of 5 mM MgCl₂ for influx studies, and in the presence or absence of 10 mM P_i, for efflux studies. Results (uptake or loss) are means±S.E.M. for one or two experiments performed in triplicate.

(a)
		Mitochondrial ATP (nmol/mg of protein)
MgCl2 concentration (mM)	Incubation time (min)…	5	10
0		0.73±0.11	1.22±0.09
5		1.26±0.06	1.96±0.09
(b)
		Mitochondrial ATP (nmol/mg of protein)
Pi concentration (mM)	Incubation time (min)…	5	10
0		−0.26±0.04	−0.41±0.08
10		−0.91±0.09	−1.04±0.04