TABLE 2.

Hydrolysis velocity and adsorption of the TrCel7A enzyme variants on HCC and PASC measured at 27 °C in 50 mm sodium acetate (pH 5.0)

The enzyme concentration was 1.4 μm, and the substrate concentration was 0.1% (w/v).

Cellulose substrate	Hydrolysis velocitya	Bound enzymeb	Specific activity of adsorbed enzymec
	μm min−1	nmol/mg of cellulose	min−1
PASC
WT
1-h time point	1.8 ± 1.1	1.4	1.3
2-h time point	1.5 ± 0.6	1.5	1.1
W40A
1-h time point	4.4 ± 1.1	1.3	3.5
2-h time point	3.0 ± 0.5	1.6	2.4
WTcat
1-h time point	1.4 ± 0.0	1.1	1.3
2-h time point	0.72 ± 0.01	1.2	0.6
W40Acat
1-h time point	0.69 ± 0.10	0.20	3.5
2-h time point	0.34 ± 0.02	0.24	1.7
HCC
WT
1-h time point	0.76 ± 0.02	0.62	1.2
2-h time point	0.47 ± 0.01	0.56	0.9
W40A
1-h time point	0.16 ± 0.00	0.30	0.5
2-h time point	0.08 ± 0.01	0.41	0.2
WTcat
1-h time point	0.21 ± 0.06	∼0.05d	4.2
2-h time point	0.15 ± 0.02	∼0.07d	2.1
W40Acat
1-h time point	0.06 ± 0.01	0.10	0.6
2-h time point	0.03 ± 0.01	0.15	0.3

^a Hydrolysis velocity, shown as cellobiose produced per min, was calculated at the 1- and 2-h time points from the progress curves shown in Fig. 2.

^b The bound enzyme concentration was determined from the supernatant after 1 and 2 h of incubation with HCC or PASC as described under “Experimental Procedures” and then dividing this concentration by the remaining cellulose amount.

^c The specific activity of the adsorbed enzyme was calculated by dividing the hydrolysis rate at the 1- and 2-h time points by the bound enzyme concentration. The uncertainty in the specific activity values was estimated to be 20% based on three repeated experiments.

^d The error was estimated to be 50% because the measured concentration was <0.1 μm. Therefore, the amounts of adsorbed WT_cat on HCC are given as rough estimates.