Fig. 3. Inhibition of human CA IX by resin acids and kinetic diagnosis of a non-competitive mechanism. (A) Concentration–response curves (0.1 nM–1 mM) for callitrisic, levopimaric, palustric and pimaric acids, with acetazolamide (AAZ) as reference. Points are mean ± SD (n = 3). (B) IC50 values (mean ± SD): AAZ 44.2 ± 1.7 nM; callitrisic acid 93.4 ± 1.6 nM; levopimaric acid 147.6 ± 4.7 nM; palustric acid 290.5 ± 15.7 nM; pimaric acid 340.7 ± 6.4 μM. (C and D) Lineweaver–Burk plots for callitrisic and levopimaric acid. Families of straight lines intersect on the x-axis, indicating unchanged Km but reduced Vmax. (E and F) Corresponding Michaelis–Menten fits for callitrisic (E) and levopimaric acid (F) showing a concentration-dependent decrease in Vmax with minimal effect on apparent Km.
