Sulfonamide Inhibition Studies of a New β-Carbonic Anhydrase from the Pathogenic Protozoan Entamoeba histolytica

A newly described β-carbonic anhydrase (CA, EC 4.2.1.1) from the pathogenic protozoan Entamoeba histolytica, EhiCA, was recently shown to possess a significant catalytic activity for the physiologic CO₂ hydration reaction (k_cat of 6.7 × 10⁵ s^-1 and a k_cat/K_m of 8.9 × 10⁷ M^-1 s^-1). A panel of sulphonamides and one sulfamate, some of which are clinically used drugs, were investigated for their inhibitory properties against EhiCA. The best inhibitors detected in the study were 4-hydroxymethyl/ethyl-benzenesulfonamide (K_Is of 36⁻89 nM), whereas some sulfanilyl-sulfonamides showed activities in the range of 285⁻331 nM. Acetazolamide, methazolamide, ethoxzolamide, and dichlorophenamide were less effective inhibitors (K_Is of 509⁻845 nM) compared to other sulfonamides investigated here. As β-CAs are not present in vertebrates, the present study may be useful for detecting lead compounds for the design of more effective inhibitors with potential to develop anti-infectives with alternative mechanisms of action.