Thermodynamics of a Ca2+ dependent, highly thermostable and detergent compatible purified alkaline serine protease from Nocardiopsis xinjiangensis strain OM-6

Extracellular alkaline protease producing salt tolerant alkaliphilic actinobacteria, Nocardiopsis xinjiangensis strain OM-6 was isolated from Okha Madi (OM) site of coastal Gujarat, India. The purified protease was stable even at 70 °C in 100 mM Ca2+ with Kd = 20 × 10−3 and t1/2 = 34 min. The activation energies (E), enthalpy (∆H*) and entropy (∆S*) for protease deactivation were 29.35 kJ/mol, 26.68 kJ/mol and −186.22 J/mol, respectively in 200 mM Ca2+. The ∆G* for protease deactivation was 97.63 kJ/mol at 50 °C in 100 mM Ca2+. OM-6 protease exhibited enhanced residual activities up to 103%, 70%, 144% and 119% with SDS, CTAB, Tween 80 and Triton X-100, respectively after 2 h of incubation at 40 °C. Interestingly, residual activity of OM-6 protease increased by 450% and 559% in 50 mM H2O2 and 10 mM β-mercaptoethanol respectively even after 2 h of incubation. Moreover, protease retained 100% of its original activity with H2O2 and β-mercaptoethanol at highest concentration after 24 h. The protease retained more than 60% of original activity with 1% w/v of each commercial detergent even after 2 h at 40 °C. These unique properties of protease make it an ideal choice for application in detergent formulations and enzymatic peptide synthesis.