Figure 7

IOS inhibition of T. reesei cellulases on ¹⁴C-cellulose substrates. (A) Binding of IOS to ¹⁴C-BC (0.25 g l^-1) (◊) or ¹⁴C-amorphous cellulose (0.5 g l^-1) (∆). IOS (0–100 μM on a reducing groups basis) were incubated with ¹⁴C-cellulose in 50 mM sodium acetate buffer, pH 5, containing BSA (0.1 g l^-1) at 35°C for 30 min. Cellulose was separated by centrifugation, and the concentration of free IOS in the supernatant ([IOS]_free) was calculated from the inhibitory strength against Tr Cel7A on MUL using the IC₅₀ value of 0.31 μM and equation 2. The concentration of IOS bound to cellulose ([IOS]_bound) was found as the difference between the total concentration of IOS and [IOS]_free. The solid lines are from the nonlinear regression analysis according to the Langmuir isotherm. (B) IOS inhibition of the synergistic hydrolysis of ¹⁴C-BC by the mixture of CBH Tr Cel7A and EG Tr Cel5A. In the case of the absence of IOS, the reaction mixture also contained N188 BG. (C) IOS inhibition of the hydrolysis of ¹⁴C-BC by CBH Tr Cel6A. (D) IOS inhibition of the hydrolysis of ¹⁴C-amorphous cellulose by EG Tr Cel7B (◊), Tr Cel5A (□), or Tr Cel12A (∆). All experiments were made in 50 mM sodium acetate buffer, pH 5.0, containing BSA (0.1 g l^-1) at 35°C. D_IOS and D_IOS=0 represent the degree of conversion of ¹⁴C-cellulose in the presence and absence of IOS, respectively. For the time courses measured in the presence and absence of IOS, see Additional file 1: Figure S1.