Abstract: In order to increase the expression level of Candida antarctica lipase B (CALB), the CALB gene was designed and synthesized according to the codon preference of Aspergillus niger, and then the CALB expression vector was constructed with PnaII/tpi as promoter and transformed into A. niger HL-1. The enzymatic activity of recombinant CALB was 171 U/mL after shaking flask fermentation for 120 h. Then, the enzymatic properties of recombinant CALB were studied. The optimum reaction temperature and pH for the enzyme were 50 ℃ and 8.0, respectively. The enzyme was very stable at pH 6.0–9.0 and temperature below 45 ℃. Its activity was strongly inhibited by 10 mmol/L Cu2+, Zn2+ and 0.1 g/100 mL SDS but was potently activated by 1 mmol/L Ca2+ and 0.1 g/100 mL sorbitol. Furthermore, the CALB was immobilized using diatomite as the carrier, and the activity of immobilized enzyme was 187 U/g under the optimal immobilization conditions. The yield of ethyl hexanoate in a solventless system was up to 91% when biosynthesized using immobilized CALB under the optimized reaction conditions.

Key words: Candida antarctica lipase B (CALB), Aspergillus niger, secretory expression, enzymatic properties, immobilization, esterification