Purification and Properties of a Lipase from Thermophilic Geobacillus stearothermophilus Strain-5

摘要

The study was aimed to purify the extracellular lipase produced from a thermophilic Geobacillus stearothermophilus strain-5. The enzyme was purified using ultrafiltration followed by three column chromatographies: Q-Sepharose ion exchange chromatography, Sephadex G-100 gel filtration and adsorption on hydroxyl apatite to 22.6-fold with 8.8% recovery. The lipase had a molecular weight of about 61 kDa. The enzyme showed optimal activity at 55-60 deg C and pH 8.0 and retained about 87.5% of its originalactivity after exposure to 70 deg C for 15 min. Furthermore, 95-100% of the original activity was retained after incubation atpH 5-9 at 60 deg C for 30 min. The presence of 1 mM of the following metal ions: Fe~(2+), Ca~(2+), Mn~(2+) and Mg~(2+) enhancethe lipase activity whereas Zv~(2+), Hg~(2+) and Cu~(2+) inhibited it. The purified enzyme exhibited good tolerance to some organic solvents especially butanol and isopropanol. The presence of detergent such as SDS, Tween 20, Tween 80 and Triton X-100 had a slight effect on the lipolytic activity. The enzyme hydrolyzes both soluble and insoluble emulsified substrates; it showed highest affinity to tributyrin. The values of K and V_(max) of the lipase using pnitrophenyl palmitate as calculated from the Linweaver-Burk plot were 0.588 mg mL~(-1) and 129.7 U mL~(-1), respectively. The obtained enzyme showed stability to different pH values, temperatures and tolerance to some detergents and organic solvents.