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Figure 3.
Fig. 3. Schematic drawing showing the CA XII dimer in the
membrane; orientation is the same as that in Fig. 2. The
extracellular CA domains (molecules A and B) are colored blue
and green, respectively. Zinc ions appear as white spheres,
disulfide linkages are yellow, and acetazolamide molecules
appear as balls-and-sticks. The yellow transmembrane helices are
modeled after the structure of the glycophorin A dimer reported
by MacKenzie and colleagues (42): both CA XII and glycophorin A
contain transmembrane GXXXG dimerization motifs (40, 41). The
intracellular C-terminal domains appear as orange spheres. These
domains contain potential phosphorylation sites but are
currently of unknown structure. Note that membrane association
orients the enzyme active sites toward the extracellular milieu,
poised for catalysis.
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