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Table 2.

Kinetic parameters (Km, Vmax)and activities of total cellulose, endo-β-1,4-glucanase andβ-1,4-glucosidase from the foregut fluid of Gecarcoidea natalis and Discoplax hirtipes

Gecarcoidea natalis
Discoplax hirtipes
EnzymeActivity (μmol min-1 ml-1)KmVmax (μmol min-1 ml-1)Activity (μmol min-1 ml-1)KmVmax (μmol min-1 ml-1)
Total cellulase 0.01±0.23 2.43 mg ml-1 cellulose 0.117 0.03±0.01   
Endo-β-1,4-glucanase 1.96±0.17 3.03 mg ml-1 CMC 6.11 1.67±0.22   
β-1,4-glucosidase       
   Uninhibited 0.655±0.11 5.84 mmol l-1 cellobiosec 0.606a 1.83±0.14 4.23 mmol l-1 cellobiosef 2.08e 
   Inhibited (20 mmol l-1glucono-d-lactone) 0.49±0.13 16.28 mmol l-1 cellobiosed 0.721a 1.22±0.13 22.87 mmol l-1 cellobioseg 2.16e 
Gecarcoidea natalis
Discoplax hirtipes
EnzymeActivity (μmol min-1 ml-1)KmVmax (μmol min-1 ml-1)Activity (μmol min-1 ml-1)KmVmax (μmol min-1 ml-1)
Total cellulase 0.01±0.23 2.43 mg ml-1 cellulose 0.117 0.03±0.01   
Endo-β-1,4-glucanase 1.96±0.17 3.03 mg ml-1 CMC 6.11 1.67±0.22   
β-1,4-glucosidase       
   Uninhibited 0.655±0.11 5.84 mmol l-1 cellobiosec 0.606a 1.83±0.14 4.23 mmol l-1 cellobiosef 2.08e 
   Inhibited (20 mmol l-1glucono-d-lactone) 0.49±0.13 16.28 mmol l-1 cellobiosed 0.721a 1.22±0.13 22.87 mmol l-1 cellobioseg 2.16e 

Activities of total cellulase, endo-β-1,4-glucanase (EG) andβ-1,4-glucosidase were measured at substrate concentrations of 13.3 mg ml-1 cellulose, 10 mg ml-1 carboxymethyl cellulose (CMC)and 29.22 mmol l-1 cellobiose, respectively. Enzyme activities are expressed as μmol glucose min-1 ml-1 digestive juice(total cellulase and β-1,4-glucosidase) or as μmol reducing sugars min-1 ml-1 (EG). Inhibited β-glucosidase from both G. natalis and D. hirtipes had a similar Vmax and a significantly higher Kmthan the uninhibited enzyme. Within a column, significant differences between values for β-glucosidase are indicated by different superscript letters. There were also significant differences in Km and Vmax between species for uninhibitedβ-1,4-glucosidase. Values are means ± s.e.m.

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