ISOLATION AND PARTIAL CHARACTERIZATION OF A NOVEL THERMOSTABLE CARBOXYLESTERASE FROM A THERMOPHILIC BACILLUS

High levels of esterase activity were detected in cell extracts from a thermophilic Bacillus. A single esterase, with an apparent molecular weight of 38,000-45,000, was purified 56-fold with 48% recovery. The partially purified esterase was fully active when assayed at 85-degrees-C and retained 90% of initial activity after exposure to a temperature of 105-degrees-C for 150 min. This enzyme, designated G18A7 esterase, showed a greater thermostability, more alkaline pH optimum (pH 9.5), and lower sensitivity to inhibitors than an esterase from Bacillus stearothermophilus strain NCA 2184, [Matsunaga, A. et al. (1974) Arch. Biochem. Biophys. 160, 504-513]. Nondenaturing polyacrylamide gel electrophoresis of samples from various stages of the purification sequence indicated that the enzyme might be present in the cell either as an aggregate of active monomers or associated with nonenzymic components.