RESUMO
The three-dimensional structure of carbonic anhydrase B (EC 4,2,1,1; carbonate hydro-lyase) from human erythrocytes has been determined to high resolution. Parallel and antiparallel pleated sheet makes up the predominant secondary structure of the enzyme. The tertiary structure is unique for its folding and is very similar to the structure is unique for its folding and is very similar to the structure of the isoenzyme, human erythrocyte carbonic anhydrase C. The essential metal ion, zinc, is firmly bound to the enzyme through three histidyl ligands and located at the bottom of a 12-A deep conical cavity. The zinc ligands are involved in a number of hydrogen bond formations with residues in the immediate vicinity of the active site cavity. Some of the similarities and differences in the sidechain orientation and active site topography of the two isoenzymes are also discussed.