FIGURE 11.

Mammalian E3 pH-dependent forward/reverse k_cat and maximal forward/reverse pH-dependent fluxes with corresponding enzyme fractional states. A, top, mammalian E3 forward k_cat as a function of pH was calculated as described under “Experimental Procedures” using globally fitted parameters (Table 1) obtained by fitting the data in Fig. 6 to the 4-state redox model. Bottom, enzyme redox fractional states corresponding to the forward k_cat in A were calculated as described under “Experimental Procedures.” B, top, mammalian E3 reverse k_cat as a function of pH was calculated in the same manner as the forward k_cat and as described under “Experimental Procedures.” Bottom, enzyme redox fractional states corresponding to the reverse k_cat were calculated as described under “Experimental Procedures.” C, top, parameterized (Table 1) 4-state redox-dependent flux expression was maximized using NAD⁺/NADH, Lipo/DHL, and pH as adjustable parameters to produce a flux maximized in the forward direction, shown as a function of pH. The lipoamide and NAD pool were constrained to 10 and 3 mm, respectively. Bottom, enzyme redox fractional states corresponding to the flux were computed with the resulting NAD⁺/NADH and Lipo/DHL ratios of 10¹² and 10⁻¹² respectively, as a function of pH. D, top, parameterized (Table 1) 4-state redox flux expression was maximized using NAD⁺/NADH, Lipo/DHL, and pH as adjustable parameters to produce a maximal flux in the reverse direction, shown as a function of pH. The lipoamide and NAD pool were constrained to 10 and 3 mm, respectively. Bottom, enzyme redox fractional states corresponding to the flux were computed with the resulting NAD⁺/NADH and Lipo/DHL ratios of 10⁻¹² and 10¹², respectively, as a function of pH. Table 2 provides the fitted parameter values for this analysis.