Figure 3. MMP-12 activity dependence on [Ca²⁺] and pH.

(A) pH-profiles of MMP-12 activity. Initial velocities [v, in rfu (relative fluorescent units)/s] of substrate cleavage by MMP-12 at pH 4.5–7.5 and four different [Ca²⁺]. The solid line is the theoretical curve obtained by non-linear regression using a model representing a singly ionizing system (eqn 2) and the dashed lines using a model with two ionizing groups (eqn 3). (B) Initial velocities of substrate cleavage by MMP-12 and different [Ca²⁺] at pH 7.5. The dotted line represents a non-linear regression fit of the one binding site model (eqn 1; n=1), the dashed line represents a fit of the two binding site model (eqn 1; n=2) and the solid line represent a fit of the three binding site model (eqn 1; n=3). The same data is plotted in a direct plot (B), and with log[Ca²⁺] (C). ■, 0.16 mM Ca²⁺; □, 1.26 mM Ca²⁺; ●, 33.6 mM Ca²⁺; ○, 200 mM Ca²⁺.