Rice carbonic anhydrase (CA) was successfully expressed as a glutathione-S-transferase (GST) fusion protein in an Escherichia coli expression system. The optimal induction concentration of IPTG and growth temperature was found to be 1.0 mM and 28 degrees C. To obtain milligram amounts of homogeneous active recombinant proteins, 150 mM NaCl and Mg-ATP solution were used during the purification procedures. After improving the conditions of expression and the purification procedures, final yield of recombinant proteins was 1.3 mg/g wet cell weight after enzymatic cleavage of the GST tag, and the molecular weight was about 29 kDa. The purified protein had CO2 hydration activity.. and had no detectable esterase activity in vitro. Addition of zinc improved the CO2 hydration activity of the rice CA produced by E coli. The effects of acetazolamide (AZ) and the anions N-3(-), NO3-, I-, Br-, and Cl- on CO2 hydration activity of CA were studied. AZ and N-3(-) were found to be strong inhibitors of rice CA. The inhibitory activity of AZ and ions was in the order AZ > N-3(-)> NO3-> I-> Br-> Cl-. (c) 2006 Elsevier Inc. All rights reserved.