Characteristics and thermodynamics of a thermostable protease from a salt-tolerant alkaliphilic actinomycete

An alkaline serine protease from a newly isolated salt-tolerant alkaliphilic actinomycetes, Brachystreptospora xinjiangensis OM-6 was purified with 35- and 26-fold purification and 47% and 22% yield employing two steps and one step methods, respectively. The enzyme was quite stable at 80 °C in 30% Na-glutamate with the deactivation rate constant (Kd) 8.66 and half life (t1/2) 80.04 min. The activation energies (E), enthalpy (ΔH*), entropy (ΔS*) and change in free energy (ΔG*) for the protease deactivation were calculated in the presence of 30% Na-glutamate and correlated with the enzyme stability. The thermodynamic analysis corresponded the trends of the enzyme stability and inactivation. The enzyme retained high activity and significant stability at higher salt, temperature, range of pH and metal ions. The enzyme was extremely resistant against urea denaturation, oxidizing and reducing agents and surfactants, a finding which is rather unique and restricted to only few proteins.