1. Surviving sheep colonic mucosal tissue incorporated l-[U−14C]threonine when incubated in Krebs medium III at 37° in an atmosphere of oxygen, into a well-characterized mucoprotein fraction, isolated by papain digestion of the incubated scrapings. 2. Acidic hydrolysis and chromatography of the labelled mucoprotein showed that threonine was the only constituent to become labelled. In the presence of puromycin the incorporation of l-[U−14C]threonine was considerably diminished (6·7 and 18·5% of control in duplicate experiments). Furthermore, puromycin also decreased incorporation of radioactivity from d-[U−14C]-glucose (48·0 and 31·6% of control) and 35SO42− (21·2 and 23·6% of control) into the mucoprotein fraction. 3. In a puromycin-inhibited system, with d-[U−14C]-glucose, where the overall specific radioactivity of the mucoprotein was 48% of control, the labelling of the individual monosaccharide constituents (as% of control) was: N-acetylneuraminic acid, 44%; N-glycollylneuraminic acid, 61%; hexosamines, 46%; fucose, 68%; galactose, 34%.
