Fig. 3

Effects of inhibitor to enzymes exerting the nonproductive binding of substrate and transglycosylation to inhibitor. a In this mechanism, a covalent glycosyl-enzyme intermediate (E _int) is included. Rates of passing through 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 inhibitor (rate constants k ₅ and k ₁₇ collectively referred to as 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 Glycosylation-limited reaction was mimicked by setting k ₂ = k ₇ = 100 s⁻¹, and k ₃ = k ₈ = 10⁴ s⁻¹. c 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 100 or 1000 s⁻¹ as defined in the legend on figure. At both k _TG values, the analyses were made by assuming the presence or absence of the nonproductive binding of substrate (the complex in yellow box omitted). d Ratios of rates measured in the presence (v _i ) and absence (v _i=0) of inhibitor as a function of inhibitor concentration. The concentration of substrate (as a multiple of its K _m value at [I] = 0) is shown in the plots. Note that there are four data series depicted in each plot on panels b–d, but some of them are not visible because of the overlap. All results presented are for the formation of the first product