[[abstract]]Several bacteria isolated from a hot spring in Yang Ming Mountain, National Park of Taiwan having the capability to degrade tributyrin. The bacterium selected for this study showed the biggest clear zone on the tributyrin agar among all samples. This thermophilic esterase producing bacterium was analyzed using l6S rDNA and partial physiological characterized; and classified as Geobacillus sp. In this study, the extracellular crude preparation was used to determine the characterization of esterase activity. The substrate specificity of the enzyme showed a preference for p-nitrophenyl acetate as compared with p-nitrophenyl myristate and p-nitrophenyl palmitate. The optimum temperature for the esterase was 60-70 DC. The enzyme retained its original activity at 60?C for a 2 h incubation period. However, enzyme activity was fully lost at 70?C for a 15 min incubation period. In addition, the p-nitrophenyl acetate assay and esterase activity staining (zymogram) showed the enzyme was active over a pH range from pH 2 to 8; with two maximal activities peaked at pH 3 and 6-7 respectively. After the crude enzyme extract mixed with the buffer (PH 3-9) and incubated for 24h at 4?C, it was stable with a ratio of 100% compared to its original activity. Among the various metal ions influence tests, esterase activities were not significantly affected. The chemical reagent, PMSF could cause a significant inhibition in the enzyme activity. The activity of the enzyme was also inhibited by SDS, Triton X-100 and Tween 20. Last, the enzyme was inhibited a 15% (v/v) concentration of ethanol and acetone; and it retained 80% activity in presence of DMSO at the same concentration of 15% (v/v). Briefly, the esterase was stable in the acidic pH region. These properties are interested and warrant for further researches on its production and molecular characterizations.
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