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 degrees 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. (c) 2004 Elsevier Ltd. All rights reserved.