Inhibition of glucose on an exoinulinase from Kluyveromyces marxianus expressed in Pichia pastoris

The INU1 gene encoding an exoinlinase from Kluyveromyces marxianus KW02 was expressed in Pichia pastoris. Enzyme activity of recombinant P. pastoris in the fermentation liquid was 52.0 U/ml, which was 12 times that of the wild type. Its apparent molecular weight was 85 kDa (SDS-polyacrylamide gel electrophoresis (PAGE)) and its theoretic molecular weight of enzymic protein was 62 kDa. The optimum pH of enzyme was 4.5. Its optimum temperature was 55 °C. Fe2+ increased the enzyme activity by 41.97%, but Mg2+ inhibitated the enzyme activity dramatically. Glucose showed competitive inhibition on enzyme activity for hydrolysis of inulin which had a degree of polymerization (DP) not less than 10, but no inhibitory effect on enzyme activity for hydrolysis of oligo-saccharide (DP ≤ 9). It was also detected that inulinase had the synthetic activity of inulin.