Figure 6

Enzymatic characterization of the effects of compound 2a on purified CSE.

(A) Lineweaver–Burk plot of CSE catalyzed H₂S production in the absence (control) and presence of various concentrations of compound 2a (5 μM, 10 μM and 20 μM). The data suggest that 2a is a competitive inhibitor, since the plots are linear and intersect at the y-axis (K_m increases while V_max remains unaffected). For reference, non-competitive inhibition would produce plots with the same x-intercept as uninhibited enzyme (K_m is unaffected) but different slopes and y-intercepts. Uncompetitive inhibition would cause different intercepts on both the y- and x-axes. The estimated V_max and K_m values are 0.50 ± 0.02 U/mg and 1.1 ± 0.1 mM. The K_{m, apparent} values are 1.5 ± 0.1 mM, 1.9 ± 0.3 mM and 2.8 ± 0.3 mM for the data at 0 mM, 5 μM, 10 μM and 20 μM of inhibitor, respectively. (B) Slopes of the double reciprocal plot vs. the concentrations of inhibitor (0, 5, 10 and 20 μM) (Fig. 6B). The intercept gives the value of K_m/V_max and the slope is K_m/(V_max K_i). K_i is obtained as the intercept/slope ratio.