Carbon bio-sequestration by anhydrase enzyme extracted from spinach (Spinacia oleracea)

Abstract

Demand for sustainable and new technologies striving for sequestration of greenhouse gases, particularly carbon dioxide, is an area of considerable focus. In recent years there has been an increased interest in using an enzyme biocatalyst, Carbonic Anhydrase (CA) for this purpose. CA is an ubiquitous metalloenzyme that catalyzes the reversible hydration of CO2 in aqueous biological systems. In this study, Carbonic Anhydrase was extracted and partially purified from a plant source which is spinach leaves. The extracted enzyme was immobilized on different materials for increased stability, recyclability and cost-effectiveness. Immobilization of Carbonic Anhydrase was done on alginate beads, chitosan beads and chitosan film. After immobilization the activities for alginate beads, chitosan beads and chitosan film were found to be 23.37, 20.96 and 17.58 U/mg respectively. Optimum pH for alginate beads and free enzyme was 8, while for chitosan beads and film it was 8.5 and 7.5 respectively. The optimum temperature for free enzyme was 30°C, while for alginate beads, chitosan beads and chitosan film it was 40°C, 35°C and 35°C respectively. For both free and immobilized enzyme, calcium carbonate precipitation was approximately same per unit of enzyme activity. The recyclability of immobilized enzyme was tested up till four cycles. The immobilized enzyme showed better stability than the free enzyme. Alginate beads, chitosan beads and chitosan film retained 76.59, 80.75 and 83% of their activities over a period of 4 weeks. It was concluded that carbonic anhydrase obtained from plant source can be used for CO2 sequestration purposes. On immobilization, the enzyme has better storage stability, recyclability and can be used in industrial process.