Figure 5.

Proton concentration-responses in the absence and presence of increasing concentrations of Ca²⁺ (a), Mg²⁺ (b), Cd²⁺ (c), Co²⁺ (d), Fe²⁺ (e), Mn²⁺ (f), Ni²⁺ (g), and Zn²⁺ (h). G_s-cAMP production was measured in transiently transfected HEK293T cells using the GloSensor cAMP assays. Metal ion stock solutions were made in water and diluted in pH preadjusted Ca²⁺/Mg²⁺ free HBSS-based buffers. Results were normalized to proton responses (%) and represented means ± SEM from a minimum of 3 independent assays, each in quadruplicate. Curves were analyzed in Prism 8.4 using the built-in four-parameter logistic function. Allosteric parameters are listed in Table 4. Dashed lines indicate relative activity at pH 7.40 or pH 7.00.