Cyanogen bromide cleavage of methionine residues as a control method for enkephalin immunocytochemistry.

Serial semithin sections of rat neurohypophysis were immunostained with 2 antibodies to enkephalins using the peroxidase antiperoxidase method. One of the antibodies (R133) recognizes both met- and leu-enkephalin whereas the other (R26) reacts with met-enkephalin only. After cyanogen bromide pretreatment of the sections the antibody R133 stained only a subpopulation of nerve endings that were distinct from those stained with the latter antibody. R26-(met-enkephalin-like) immunoreactivity was totally abolished by cyanogen bromide pretreatment. This preincubation method which selectively interferes with the staining of met-enkephalin terminals may help to discriminate the two enkephalins in immunocytochemical preparations.