Fig. 4

Effects of inhibitor to enzymes exerting the nonproductive binding of substrate and transglycosylation to substrate. a In this mechanism, a covalent glycosyl-enzyme intermediate (E _int) is included. Rates of passing through the elementary steps are represented by rate constants and concentration terms above corresponding arrows. After the formation (rate constants k ₂ and k ₇), E _int can break down by hydrolysis (rate constants k ₃ and k ₈) or by the transglycosylation to substrate (rate constant k _TG). The steady-state solution was analyzed numerically. The values of the off-rate constants for the dissociation of the noncovalent complexes were set to 10⁴ and 10⁵ s⁻¹ for the dissociation of substrate and inhibitor, respectively. The values of all the second-order rate constants were set to 10³ mM⁻¹ s⁻¹. b The dependency of the ratio of steady-state velocity to the total enzyme concentration from the concentration of substrate. c Ratios of rates measured in the presence (v _i ) and absence (v _i=0) of inhibitor as a function of the inhibitor concentration. The concentration of substrate (as a multiple of its K _m value at [I] = 0, or as a multiple of its concentration at optimum in the case of the rightmost plot) is shown in the legend on figure. In panels b and c, the glycosylation-limited reaction was mimicked by setting k ₂ = k ₇ = 100 s⁻¹, and k ₃ = k ₈ = 10⁴ s⁻¹. The deglycosylation-limited reaction was mimicked by setting k ₂ = k ₇ = 10⁵ s⁻¹, and k ₃ = k ₈ = 100 s⁻¹. In both cases, the value of k _TG was set either 10 s⁻¹ or 1000 s⁻¹ as defined in the plots. All results presented are for the formation of the first product