CARBONIC-ANHYDRASE ISOENZYME-II IS LOCATED IN CORTICOTROPHS OF THE HUMAN PITUITARY-GLAND

We studied the location of carbonic anhydrase (CA) isoenzymes I, II, a nd VI in human pituitary gland using specific antisera in conjunction with immunoblotting, immuneperoxidase, and double immunofluorescence s taining techniques, Stainings with anti-CA II serum showed intense cyt oplasmic reaction in the anterior lobe of the pituitary gland. Double immunofluorescence staining was used to identify the cells that expres sed CA II. Confocal laser scanning microscopy revealed that, of the an terior pituitary hormones studied, ACTH coincides mainly with CA II in these cells. Stainings with anti-CA I and VI sera were negative in th e endocrine cells of the pituitary gland. Western blotting of the pitu itary gland with anti-CA II revealed a distinct 29-KD polypeptide band corresponding in molecular weight to CA II, suggesting that the antis erum does not detect any nonspecific protein, Anti-CA I serum similarl y showed a major 29-KD band, possibly recognizing the enzyme, which is abundantly present in erythrocytes. The results indicate that CA II i s expressed in corticotrophs of human pituitary gland, in which its ph ysiological role may be linked to the regulation of optimal pH in the secretory vesicles for the cleavage of ACTH from its precursor.