Uptake of [3H]threonine in human colonic mucosa associated with carcinoma: an autoradiographic analysis at the ultrastructural level.

The uptake of D,L-[G-3H]threonine was studied to show cellular protein synthesis, at the ultrastructural level, as part of our investigation into alterations in glycoprotein synthesis which occur in colonic mucosa adjacent to carcinoma ('transitional' mucosa). Threonine uptake, though variable, was higher in 'transitional' than in normal mucosa. Most of the threonine was incorporated into the endoplasmic reticulum of the immature cells at the bottom of the crypt. With longer isotope incubation, activity was found in other organelles in cells which were still undifferentiated or immature or both. From our data, the increased uptake of [3H]threonine in 'transitional' mucosa, seems to be the result of prolonged protein synthesis associated with an extension of the cellular proliferation zone in the crypt, rather than being the effect of increased cell turnover. Thus, variations in [3H]threonine uptake are not related to the changes in the rate of galactose incorporation in mucosa adjacent to carcinoma.