Figure 2.

Comparison of deduced amino acid sequences for CA IV from cow, rabbit, human, mouse, and rat. ▿, Sites at which the leader peptide is cleaved. This proteolytic cleavage site is tentative in murine and rat CA IVs. ▾, Sites at which the hydrophobic tail is cleaved, based on agreement with common features for glycosylphosphatidylinositol (GPI)-anchored proteins. Sixteen of the 17 amino acid residues, thought to be near the “active sites” and common to nearly all CAs, are boxed. ↓, Conserved histidine implicated in proton transfer. ∗, Three potential zinc-binding histidines. ○, Four cysteines that are involved in intramolecular disulfide bond formation. The putative N-glycosylation sites defined by the tripeptide consensus sequence of Asn-Xaa-Thr/Ser are underlined. The amino acid residues that were engineered by site-directed mutagenesis are indicated by boldface type.