| Summary: | 碩士 === 大同大學 === 生物工程學系(所) === 101 === Due to the concerns of fossil oil shortage, development of alternative energy sources has long been the focus of research. In this study, heterologous expression and biochemical properties of a lipase which can be potentially used for biodiesel production was investigated. lipA and lipB encoding lipase and lipase-specific foldase, respectively, were cloned from Burkholderia sp. and heterologously expressed in E. coli. lipA bearing the DNA sequence for its original signal peptide or that with corresponding sequence replaced by pelB leader sequence was constructed along with lipB onto expression vectors pHlipAB26 and ppelBHnosLipAB26. After 18 h induction by IPTG, maximal expression of 38,000 and 50,000 U/L, respectively, was achieved. SDS-PAGE and Western blotting analyses indicated that signal peptides for active lipases were removed, resulting in production of nosLipA and HnosLipA having molecular weights of 33.1 and 34.1 kDa and specific activities of 1302 and 1061 U/mg, respectively. Both lipases displayed the highest hydrolysis activity toward p-nitrophenyl laurate. The temperature optimum for nosLipA and HnosLipA were both at 50oC, while Tm values (the temperature at which 50% activity was remained after 1 h incubation) were 47.5 and 46oC, respectively. The optimal pH was 10 and 9.5, respectively, while the best pH stability were both at 8.0. Pre-treatment of 20% (v/v) n-butanol could only improve nosLipA activity, but Ca2+, 0.1% (v/v) Tween 40, Tween 80, Triton X-100 and SDS enhanced activities for both lipases. Cell extracts of recombinant E. coli carrying pHlipAB26 and ppelBHnosLipAB26 were capable of catalyzing transesterification of soybean oil. Under the conditions examined, a 4:1 molar ratio of no70LipB lacking N-terminal 70 amino acids of LipB to LipA could assist in vitro refolding of inactive LipA with the best recovery of the specific activity of 4 U/mg.
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