title: Purification and physicokinetic characterization of a gluconolactone inhibition-insensitive β-glucosidase from Andrographis paniculata nees. Leaf.
abstract: A gluconolactone inhibition-insensitive β-glucosidase from Andrographis paniculata (Acanthaceae) leaves has been isolated, homogeneity purified, and characterized for its physicokinetic properties. The purified enzyme appeared to be a monomeric structure with native molecular weight about 60 kD. The enzyme exhibited optimum pH 5.5 and pI 4.0, meso-thermostability and high temperature optimum (55°C) for catalytic activity, with activation energy of 6.8 kcal Mol(-1). The substrate saturation kinetics studies of the enzyme revealed a Michaelis-Menten constant (Km) of 0.25 mM for pNPG and catalytic efficiency (Kcat/Km) of 52,400 M (-1) s(-1), respectively. Substrate specificity of the enzyme was restricted to β-linked gluco-, manno- and fuco-conjugates. The gluconolactone inhibition insensitivity was evident from its very low inhibition at millimolar inhibitor concentrations. Interestingly, the enzyme showed geraniol transglucosylating activity with pNPG as glucosyl donor but not with cellobiose. The catalytic activity of the enzyme has been reported to be novel with respect to its activity and preferences from a medicinal plant resource.
authors.affiliation: Central Institute of Medicinal and Aromatic Plants Council of Scientific and Industrial Research, Lucknow, India.
authors.forename: Siddhartha Kumar
authors.initials: SK
authors.lastname: Mishra
authors.forename: Neelam Singh
authors.initials: NS
authors.lastname: Sangwan
authors.forename: Rajender Singh
authors.initials: RS
authors.lastname: Sangwan
mesh_terms: D035685:Andrographis / Q000201:enzymology*; D002475:Cellobiose / Q000737:chemistry; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000737:chemistry; D004795:Enzyme Stability; D005942:Gluconates / Q000737:chemistry*; D006031:Glycosylation; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007783:Lactones / Q000737:chemistry*; D008970:Molecular Weight; D018515:Plant Leaves / Q000201:enzymology*; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification; D013379:Substrate Specificity; D001617:beta-Glucosidase / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D004791:Enzyme Inhibitors; D005942:Gluconates; D007783:Lactones; D010940:Plant Proteins; D002475:Cellobiose; D001617:beta-Glucosidase; C010730:beta-glucono-1,5-lactone