FIGURE 3.

Dependence of kinetic cooperativity on Mg²⁺ concentration in four CBS-PPases. The panels show (from top to bottom) the catalytic constant k_cat, the Michaelis constants K_m1 and K_m2, and the Hill coefficient h. The enzyme identities are indicated on the top of the panels. Values of k_cat were fit to the equation k_cat = k_cat,0 + (k_cat,M − k_cat0)/{1 + (K_M/[M])ⁿ} (with n equal to 1 and 2 for cnPPase and cpPPase, respectively) where k_cat,0 and k_cat,M are the limiting values of k_cat at zero and infinite Mg²⁺ concentrations, respectively, and K_M is the metal binding constant. The lines for K_m1 and K_m2 show the best fits for Equation 6. The horizontal dotted lines (h = 1) mark the boundary between positive and negative cooperativity. K_m values are measured in terms of the MgPP_i complex. Error bars represent S.E.