TABLE 1.

Michaelis-Menten parameters for hydrolysis of nitrophenyl-β-d-xylopyranoside and xylooligosaccharide substrates by Thermoanaerobacterium saccharolyticum β-xylosidase

SubstrateConcn range (μM)Km (mM)kcat (s−1)kcat/Km (mM−1 · s−1)
p-Nitrophenyl-β-d-xylopyranosidea10-2500.09 ± 0.014.2 ± 0.247 ± 6
150-2,0000.81 ± 0.1913 ± 1.416 ± 4
o-Nitrophenyl-β- d-xylopyranosidea6-3750.08 ± 0.012.8 ± 0.135 ± 5
150-2,0000.36 ± 0.065.1 ± 0.3214 ± 2
Xylobiosea104-2,0803.3 ± 0.72.7 ± 0.40.82 ± 0.21
2,080-16,00010.2 ± 0.75.6 ± 0.20.55 ± 0.04
Xylotrioseb52-12,0000.143 ± 0.0112.0 ± 0.114 ± 1.2
  • a Km and kcat were calculated at both lower- and higher-substrate-concentration ranges due to deviation from Michaelis-Menten kinetics at higher substrate concentrations.

  • b Kinetic parameters were obtained from nonlinear fitting to the Michaelis-Menten equation with substrate inhibition (equation 3). The Ki for xylotriose was 1.7 ± 0.1 mM.