Biochemical characterization of a novel thermostable xyloglucanase from an alkalothermophilic Thermomonospora sp.

Abstract

Xyloglucanase from an extracellular culture filtrate of alkalothermophilic Thermomonospora sp. was purified to homogeneity with a molecular weight of 144kDa as determined by SDS-PAGE and exhibited specificity towards xyloglucan with apparent K (m) of 1.67mg/ml. The enzyme was active at a broad range of pH (5-8) and temperatures (40-80°C). The optimum pH and temperature were 7 and 70°C, respectively. The enzyme retained 100% activity at 50°C for 60h with half-lives of 14h, 6h and 7min at 60, 70 and 80°C, respectively. The kinetics of thermal denaturation revealed that the inactivation at 80°C is due to unfolding of the enzyme as evidenced by the distinct red shift in the wavelength maximum of the fluorescence profile. Xyloglucanase activity was positively modulated in the presence of Zn(2+), K(+), cysteine, β-mercaptoethanol and polyols. Thermostability was enhanced in the presence of additives (polyols and glycine) at 80°C. A hydrolysis of 55% for galactoxyloglucan (GXG) from tamarind kernel powder (TKP) was obtained in 12h at 60°C and 6h at 70°C using thermostable xyloglucanases, favouring a reduction in process time and enzyme dosage. The enzyme was stable in the presence of commercial detergents (Ariel), indicating its potential as an additive to laundry detergents.