Radloimmunoassay of intestinal goblet cell mucin

A double-antibody radioimmunoassay was developed for the measurement of rat intestinal goblet cell mucin. Labeling of the mucin was achieved by mild periodate oxidation and sodium boro[3H]hydride reduction using the technique of Van Lenten and Ashwell [(1971)] J. Biol. Chem.246, 1889–1894]. Tracer amounts (0.5 ng) of labeled mucin were incubated with specifie rabbit antibody in the presence of unlabeled mucin standards or extracts of intestinal tissues or their secretions. Normal rabbit serum and sheep antiserum to rabbit IgG (in a ratio of 1:10, v/v) were used as a double-antibody system to precipitate the mucin-antibody complex. The radioimmunoassay proved to be suitable for measuring 3–80 ng of mucin in intestinal homogenates (soluble fraction), acid-precipitable glycoprotein (after solubilization and neutralization), and purer mucin fractions prepared by precipitation of homogenate supernatant solutions with cetyltrimethylammonium bromide. To our knowledge this is the first study in which a mucin has been measured by means of a radioimmunoassay.