Mutation of amino acid residues 94, 96 and 119 to histidine(s) in the human carbonic anhydrase (CA, EC 18.104.22.168) related proteins CARP VIII, X and XI restored the zinc binding and catalytic activity for the hydration of CO(2) to bicarbonate. CA VIII, X and XI thus obtained showed high catalytic activity (67.3-92.0% of the activity of hCA II and much higher compared to hCA I) and were inhibited in the milli-micromolar range by inorganic anions, sulfamide, sulfamic acid, phenylboronic acid and phenylarsonic acid. Among the three new isoforms, hCA X was the most efficient enzyme and also showed the highest affinity for anion inhibitors (K(I)s of 3.6-68 μM for phenylboronic acid, sufamic acid, sulfamide, cyanide and azide). hCA VIII was poorly inhibited by halides, cyanate, nitrate and sulfate (K(I)s of 38.4-65.4 mM), whereas CA XI had a behavior intermediate between that of hCA VIII and X, both regarding the catalytic activity and sensitivity to anion inhibitors.
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