Chiang Mai Journal of Science

Extracellular lipases from thermophilic bacterial isolates P1, TP404 and TP811 were compared to their clones in E. coli DH5a named pUC-P1, pUC-TP404 and pUC-TP811 in terms of activity and stability in the presence of some metal ions, inhibitors and surfactants. All the thermostable lipolytic activities were not affected by 10 mM concentration of Na⁺, K⁺, Ca²⁺ and Pb²⁺ after being pre-incubated at 30°C for 24 h but they were inhibited by Co²⁺, V²⁺ and Ag⁺ at the same conditions. The enzymes were not inactivated by 10 mM of the chelating agents ethylenediaminetetraacetate (EDTA) and ethyleneglycol-bis [-aminoethylether]-N, N, N’, N’- tetraacetic acid (EGTA). The lipase activities were partially inhibited by 10 mM of phenylmethylsulfonyl fluoride (PMSF) whereas 2-mercaptoethanol had no significant inhibition. Enzyme activities were increased about 2 folds in the presence of 3 M urea and 4% (v/v) octylphenoxypolyhydroxyethanol (Triton X-100) but strongly inhibited by 0.5% (w/v) of sodiumdodecyl sulfate (SDS). The results demonstrated that all of these lipases are not metalloproteins. Serine residue may be present at the active site but no disulfide bridge is found necessary for the catalytic function . In general, properties of the recombinant enzymes are not different from these of the native ones indicating that the molecular cloning process is successful. However, further studies are needed to confirm this point and to investigate potential applications of the enzymes.