A thermoalkaliphilic halotolerant esterase from Rhodococcus sp. LKE-028 (MTCC 5562): Enzyme purification and characterization

A newly isolated Rhodococcus sp. LKE-028 (MTCC 5562) from soil samples of Gangotri region of Uttarakhand Himalayan produced a thermostable esterase. The enzyme was purified to homogeneity with purification fold 62.8 and specific activity 861.2 U mg^?1 proteins along with 26.7% recovery. Molecular mass of the purified enzyme was 38 kDa and values of K_m and V_max were 525 nM and 1666.7 U mg^?1 proteins, respectively. The esterase was active over a broad range of temperature (40–100 °C) and pH (7.0–12.0). The esterase was most active at pH 11.0. The optimum temperature of enzyme activity was 70 °C and the enzyme was completely stable after 3 h pre-incubation at 60 °C. Metal ions like Ca²⁺, Mg²⁺ and Co²⁺ stimulated enzyme activities. Purified esterase remarkably retained its activity with 10 M NaCl. Enzyme activity was slightly increased in presence of non-polar detergents (Tween 20, Tween 80 and Triton X 100), and compatible with oxidizing agents (H₂O₂) and reducing agents (β-mercaptoethanol). Activities of the enzyme was stimulated in presence of organic solvents like DMSO, benzene, toluene, methanol, ethyl alcohol, acetone, isoamyl alcohol after 10 days long incubation. The enzyme retained over 75% activity in presence of proteinase K. Besides hyperthermostability and halotolerancy the novelty of this enzyme is its resistance against protease.