Immunohistochemical localization of the pro-opiomelanocortin-gene product, glycylglutamine, in the intermediate pituitary

Glycylglutamine, the car☐yterminal sequence of β-endorphin_1–31, is produced as a free dipeptide during the posttranslational synthesis of β-endorphin_1–27. Antisera which recognize glycylglutamine were raised in rabbits and used for immunohistochemistry. With these antisera, glycylglutamine immunoreactivity was demonstrated in cells of the rat intermediate pituitary. In contrast, anterior pituitary cells, which exhibited β-endorphin immunoreactivity, did not react with the anti-glycylglutamine sera. The conclusion that the antisera distinguished glycylglutamine immunoreactivity from β-endorphin_1–31 immunoreactivity is based upon cellular specificity, fixation requirements and blocking studies. The antisera demonstrated the differential expression of this dipeptide product of the proopiomelanocortin prohormone. The efficacy of carbodiimide as an immunohistochemical fixative for small molecules is also known.