Modulation of rat salivary carbonic anhydrase by pilocarpine

Carbonic anhydrase (CA) from pilocarpine-treated (1.5 mg/kg body weight; i.p.) rat saliva was purified by inhibitor affinity chromatography. The purified CA contained Mr 42000 and 39000 proteins on sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition to the erythrocyte isozyme (Mr 30000), salivary gland CA from rats without pilocarpine stimulation contained Mr 39000 and 33000 proteins and that from rats with pilocarpine stimulation also contained Mr 42000 protein. The 42000Da and 39000Da proteins bound to concanavalin A and were cleaved by endo-beta-N-acetylglucosaminidase F to become 39000Da and 33000Da proteins. These results suggest that, under the influence of pilocarpine, salivary gland cells synthesize a new glycoprotein, Mr 42000, via N-linked glycosylation of a 39000Da glycoprotein, which is the only secretory glycoprotein in the unstimulated salivary gland and is produced by N-linked glycosylation of a 33000Da polypeptide.