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

Abstract

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 100mM Ca²⁺ with K_d=20×10^-3 and t_1/2=34min. The activation energies (E), enthalpy (∆H*) and entropy (∆S*) for protease deactivation were 29.35kJ/mol, 26.68kJ/mol and -186.22J/mol, respectively in 200mM Ca²⁺. The ∆G* for protease deactivation was 97.63kJ/mol at 50°C in 100mM 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 2h of incubation at 40°C. Interestingly, residual activity of OM-6 protease increased by 450% and 559% in 50mM H₂O₂ and 10mM β-mercaptoethanol respectively even after 2h of incubation. Moreover, protease retained 100% of its original activity with H₂O₂ and β-mercaptoethanol at highest concentration after 24h. The protease retained more than 60% of original activity with 1% w/v of each commercial detergent even after 2h at 40°C. These unique properties of protease make it an ideal choice for application in detergent formulations and enzymatic peptide synthesis.

Keywords: Calcium dependent; Detergent compatible protease; Salt-tolerant alkaliphilic actinobacteria; Thermodynamics and kinetics.