β-glucosidase from Withania somnifera (Solanaceae) leaf has been purified to homogeneity and characterized for its physico-kinetic properties. The enzyme purification was achieved through a sequence of gel filtration and ion-exchange column chromatography, and PAGE revealed the homogeneity purification status of the enzyme. The properties of the enzyme included an acidic pH optima (4.8), alkaline pI (8.7), meso-thermostabity, monomeric structure with subunit molecular weight of about 50 kDa, high affinity for substrate (Km) for pNPG (0.19 mM) and high (105,263 M-1 s-1) catalytic efficiency (Kcat/Km). The mesostable enzyme had a stringent substrate specificity restricted only to β-linked gluco-conjugate. The enzyme is optimally active at 40 ºC with 12.4 kcal Mol-1 activation energy, and was highly sensitive to D-gluconic acid lactone inhibition (94 % at 1 mM) with an apparent Ki 0.21 mM. The enzyme could catalyze transglucosylation of geraniol with pNPG as glucosyl donor, but not with cellobiose. Some of the physico-kinetic properties were noted to be novel when comprehensively compared with its counterparts from plant, animal and microbial counterparts. Nevertheless, the catalytic and other features of the enzyme were relatively closer to Oryza sativa among plants and Talaromyces thermophillus among fungi. Significance of building-up of a library of novel plant β-glucosidases for structural investigation to understand naturally evolved mechanistics of catalysis has been indicated.
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