Carbonic anhydrases (CAs) have been given much attention as biocatalysts for CO2 sequestration process because of their ability to convert CO2 to bicarbonate. Here, we expressed codon-optimized sequence of alpha-type CA cloned from Dunaliella species (Dsp-aCAopt) and characterized its catalyzing properties to apply for CO2 to calcite formation. The expressed amount of Dsp-aCAopt in Escherichia coli is about 50 mg/L via induction of 1.0 mM isopropyl-beta-d-thiogalactopyranoside at 20 A degrees C (for the case of intact Dsp-aCA, negligible). Dsp-aCAopt enzyme shows 47 A degrees C of half-denaturation temperature and show wide pH stability (optimum pH 7.6/10.0). Apparent values of K (m) and V (max) for p-nitrophenylacetate substrate are 0.91 mM and 3.303 x 10(-5) mu M min(-1). The effects of metal ions and anions were investigated to find out which factors enhance or inhibit Dsp-aCAopt activity. Finally, we demonstrated that Dsp-aCAopt enzyme can catalyze well the conversion of CO2 to CaCO3, as the calcite form, in the Ca2+ solution [8.9 mg/100 mu g (172 U/mg enzyme) with 10 mM of Ca2+]. The obtained expression and characterization results of Dsp-aCAopt would be usefully employed for the development of efficient CA-based system for CO2-converting/capturing processes.