Purification and characterization of arsenite oxidase from Arthrobacter sp.

The chemolithoautotroph, Arthrobacter sp.15b oxidizes arsenite to arsenate using a membrane bound arsenite oxidase. The enzyme arsenite oxidase is purified to its homogeneity and identified using MALDI-TOF MS analysis. Upon further characterization, it was observed that the enzyme is a heterodimer showing native molecular mass as ~100 kDa and appeared as two subunits of ~85 kDa LSU and 14 kDa SSU on SDS–PAGE. The V _max and K _m values of the enzyme was found to be 2.45 μM (AsIII)/min/mg) and 26 μM, respectively. The purified enzyme could withstand wide range of pH and temperature changes. The enzyme, however, gets deactivated in the presence of 1 mM of DEPC suggesting the involvement of histidine at the binding site of the enzyme. The peptide analysis of large sub unit of the enzyme showed close match with the arsenite oxidases of Burkholderia sp. YI019A and arsenite oxidase, Mo-pterin containing subunit of Alcaligenes faecalis. The small subunit, however, differed from other arsenite oxidases and matched only with 2Fe–2S binding protein of Anaplasma phagocytophilum. This indicates that Rieske subunits containing the iron–sulfur clusters present in the large as well as small subunits of the enzyme are integral part of the protein.