Fig. 3.

Lack of competition between Na⁺ and H⁺ transport reactions. Dependencies of Na⁺ and H⁺ transport on pH (A and B, respectively) and Na⁺ concentration (C and D, respectively). Values of pH and Na⁺ concentration are shown in B and D as curve labels. The Na⁺ transport reaction time was 15 s. The buffers used were MES- (pH 5.5), MOPS- (pH 6.0, 7.2, and 8.0), or CAPSO-TMA (pH 9.0). Na⁺ transport was measured with 1 mM Na⁺, 50 mM K⁺, and the following Mg²⁺/TMA₄⋅PP_i concentrations: 13.1/9.8, 6.6/1.0, and 6.5/0.8 mM at pH 5.5, 7.2, and 9.0, respectively. H⁺ transport measurements were performed in the presence of 10 mM Na⁺, 50 mM K⁺, and the following Mg²⁺/TMA₄⋅PP_i concentrations: 8.8/4.65, 6.6/1.42, 5.8/0.47, 5.7/0.43, and 5.7/0.42 mM at pH 5.5, 6.0, 7.2, 8.0, and 9.0, respectively. Other conditions were as described for Fig. 2.