Purification, Characterization and Thermodynamic Assessment of an Alkaline Protease by Geotrichum Candidum of Dairy Origin

BACKGROUND: Alkaline proteases is the important group of enzymes having numerous industrial applications including dairy food formulations. OBJECTIVES: The current study deals with the purification and characterization of an alkaline serine protease produced by Geotrichum candidum QAUGC01, isolated from indigenous fermented milk product, Dahi. MATERIAL AND METHODS: In total twelve G. candidum strains were screened for their proteolytic activity by using standard protease assay. The protease production from G. candidum QAUGC01 was optimized by varying physio-chemical conditions. The protease was purified by using two-step method: ammonium sulfate precipitation and gel filtration chromatography. Protease was further characterized by studying various parameter like temperature, pH, modulators, metal ions and organic solvent. A thermodynamic study was also carried out to explore the half-life of protease. RESULTS: The G. candidum grew profusely at 25 °C and at an initial pH of 4.0 for 72 h of incubation producing 26.21 U/ml maximum extracellular protease. Protease revealed that V(max) and K(m) was 26.25 U.ml(-1).min(-1) and 0.05 mg.mL(-1), respectively using casein as substrate. The enzyme was stable at a temperature range (25–45 °C) and pH (8–9). Residual enzyme activity was strongly inhibited in the presence of PMSF (7.5%). The protease could hydrolyze proteinaceous substrates, casein (98%) and BSA (95%). The thermodynamic studies explored that the half-life of the enzyme that was 106.62 min, 38.72 min and 15.71 min at 50, 60 and 70 °C, respectively. CONCLUSIONS: Purified protease from G. candidum GCQAU01 is an ideal candidate for industrial application.