Improved biotransformation of arsenic by arsenite oxidase - Chitosan nanoparticle conjugates

Recent developments in the potential use of nanoparticles as carriers of enzyme have attracted great attention. In the present study, arsenite oxidase (AOase) enzyme capable of transforming the more toxic arsenite [As(III)] to the less toxic arsenate [As(V)] was extracted from an arsenic resistant bacterium (Exiguobacterium sp. As-9) and partially purified. Chitosan nanoparticles were prepared on the basis of ionic gelation of chitosan with tripolyphosphate (TPP) anions. The purified AOase was immobilized efficiently by physical adsorption on to chitosan nanoparticles and were characterized for particle size, morphology, zeta potential, AOase loading efficiency and in vitro transformation assay. The chitosan nanoparticles were spherical in shape with the average diameter of 100nm which increased to 294nm upon successful loading of AOase. Under optimized conditions, the loading capacity of the chitosan nanoparticle was determined to be 71% for AOase. Further, immobilization also increased the stability of AOase at varying temperature (4-37°C) and pH (5-10) for a period of 30days with the increased enzymatic activity (159.57Uml^-1). It also facilitated increased biotransformation (89%) of As(III) to As(V). A conceptual understanding of biological responses to AOase loaded chitosan nanoparticles is needed for the development of novel methods of drug delivery.