Saccharomyces cerevisiae β-Carbonic Anhydrase: Inhibition and Activation Studies

The β-carbonic anhydrase from Saccharomyces cerevisiae (CA, EC 4.2.1.1), scCA, which is encoded by the Nce103 gene, is an effective catalyst for CO2 hydration to bicarbonate and protons, with a kcat of 9.4 x 105 s-1, and kcat/KM of 9.8 x 107 M-1.s-1. Its inhibition with anions and sulfonamides has been investigated, as well as its activation with amines and amino acids. Bromide, iodide and sulfamide, were the best anion inhibitors, with KIs of 8.7 - 10.8 μM. Benzenesulfonamides substituted in 2-, 4- and 3,4-positions with amino, alkyl, halogeno and hydroxyalkyl moieties had KIs in the range of 0.976 - 18.45 μM. Better inhibition (KIs in the range of 154 - 654 nM) was observed for benzenesulfonamides incorporating aminoalkyl/carboxyalkyl moieties or halogenosulfanilamides; benzene- 1,3-disulfonamides; simple heterocyclic sulfonamides and sulfanilyl-sulfonamides. The clinically used sulfonamides/sulfamate (acetazolamide, ethoxzolamide, methazolamide, dorzolamide, topiramate, celecoxib, etc.) generally showed effective scCA inhibitory activity, with KIs in the range of 82.6 - 133 nM. The best inhibitor (KI of 15.1 nM) was 4-(2-amino-pyrimidin-4-yl)-benzenesulfonamide. Ladrenaline and some piperazines incorporating aminoethyl moieties were the most effective scCA activators. These studies may lead to a better understanding of the role of this enzyme in yeasts/fungi, and since the Nce103 gene is also present in many pathogenic organisms (Candida spp., Cryptococcus neoformans, etc) they may be useful to develop antifungal drugs.