Figure 10

The response of three types of ligand binding to divalent cation type and concentration (Mg²⁺ black, Mn²⁺ pink; Co²⁺ royal blue; Ni²⁺ light blue). Left) K_a-PEP values. Right) K_ix values for both Ala (filled circles) and Fru-1,6-BP binding (open squares). Importantly, because data were collected by observing enzymatic response and enzymatic turnover is thought to depend on the presence of divalent cation, even at low divalent cation we anticipate that a divalent cation was present in the active site reporting function. Values were derived from Figs. 5, 6, 7 and 8 and fits to Eq. (2). Error bars represent error estimates obtained from data fits and when not visible, they are smaller than data points. Note that a reduced allosteric response makes it more challenging to evaluate K_ix-Ala (i.e., see 5 and 10 mM Ni²⁺, where the response to Ala changes from allosteric inhibitor to allosteric activator), resulting in more noise in the data trend.