Purification and characterization of amidase from Paracoccus sp. SKG: Utilization of amidase-inhibited whole cells for bioconversion of acrylonitrile to acrylamide

•Purification and characterization of amidase enzyme from Paracoccus sp. SKG.•Amidase inhibited whole cells used as biocatalyst for biotransformation.•Optimised the conditions for biotransformation of acrylonitrile to acrylamide.•Production of acrylamide by Paracoccus sp. SKG.

A bacterial strain, Paracoccus sp. SKG, capable of utilizing aliphatic nitriles as a sole source of carbon and nitrogen was isolated. Degradation of nitriles follows a bi-enzymatic pathway with the successive action of nitrile hydratase (NHase) and amidase. The inducible enzyme, amidase from cell-free extract of Paracoccus sp. SKG, was purified and characterized. The amidase was purified to 43.7 fold with a recovery of 46.5% yield and an estimated molecular mass of 90 kDa. The purified amidase exhibits the highest activity at pH 7.5 and temperature of 50 °C. This enzyme is highly specific to aliphatic amides with the highest activity to acetamide, propionamide and acrylamide, but not to aromatic amides. Among the metal ions studied, Mn2+, Mg2+ and Ni2+ ions increase the enzyme activity, whereas Cu2+ completely inhibits it. In vitro inhibition of amidase was confirmed by preincubation of the whole cells with Cu2+. The use of whole cells of Paracoccus sp. SKG was demonstrated as a biocatalyst for the bioconversion of acrylonitrile to acrylamide in a batch reaction. The bioconversion of acrylonitrile to acrylamide resulted in 27 g/L of acrylamide with 65% of conversion under optimal conditions of pH (7.5) and temperature (30 °C).

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