Abstract
Carbonic anhydrases (CAs) are ubiquitous metallo-enzymes that catalyse the reversible hydration of carbon dioxide to bicarbonate and proton. In humans there are 15 isoforms among which only 12 are catalytically active. Since active human (h) CAs show different efficiency, the understanding of the molecular determinants affecting it is a matter of debate. Here we investigated, by a site-specific mutagenesis approach, residues modulating the catalytic features of one of the least investigated cytosolic isoform, i.e. hCA XIII. Results showed that residues assisting the formation of an ordered solvent network within the catalytic site as well as those forming a histidine cluster on the protein surface are important to guarantee an efficient proton transfer.