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The extracellular dextransucrase produced from Pediococcus pentosaceus, a new isolate from the soil in Assam, India, was purified and characterized. The enzyme activity of cell-free supernatant was 3.4 U/mL and specific activity was 0.6 U/mg. The crude enzyme was purified by a single-step fractionation using polyethylene glycols of different molecular mass. The specific activity achieved was 18 U/mg with 31-fold purification by PEG 400 and 26 U/mg with 45-fold purification by PEG 1500. The molecular mass of dextransucrase determined by non-denaturing SDS-PAGE was approx. 180 kDa. The dextran formation activity of the enzyme was confirmed by activity staining. Optimum conditions for dextransucrase activity were: pH=5.4, reaction temperature 30 °C, 5 % sucrose and 20 mM sodium acetate buffer. A concentration of 1 mM MgCI2 and 6 mM CaCl2 enhanced dextransucrase activity by 5 and 150 %, respectively. The chaotropic agent urea (7 M) and chelating agent EDTA (1 mM) resulted in the residual enzyme activity of 98 and 80 %, respectively. The organic solvents such as ethanol (50 %), DMSO (90 %), acetone (50 %) and acetonitrile (20 %) decreased the dextransucrase activity by 80, 91, 94 and 80 %, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Dextran produced by a natural isolate of Pediococcus pentosaceus, screened from Assam, in the Northeastern region of India, was estimated, purified, structure characterised and functionality analysed. The dextran concentration in the cell free supernatant of the isolate P. pentosaceus was 10.2mg/ml. FT-IR analysis revealed the hydroxyl and carboxyl functional groups present in the dextran. 1H NMR and 13C NMR spectral data revealed that the dextran has a linear backbone of α-(1→6) linked d-glucose residues. The decrease in viscosity of dextran solution with the increase in shear rate, threw light on its typical non-Newtonian pseudoplastic behaviour. The cytotoxicity tests on human cervical cancer (HeLa) cell line was studied which showed the dextran is non-toxic and biocompatible, rendering it safe for drug delivery, tissue engineering and various other biomedical applications. [Copyright &y& Elsevier]