Studies on the incorporation of radioactive amino acids into tissue and brush border membrane proteins of mouse jejunum in organ culture.

1. The incorporation of radioactive amino acids into brush border membrane proteins of mouse jejunal mucosa has been investigated in organ culture and compared to similar data obtained in intestinal culture of other species. 2. Amino acid precurosor pools for protein synthesis remained almost unchanged during 24 hr culture. 3. By pulse experiments, it has been possible to show a constant rate of protein synthesis up to 24 hr culture. 4. Continuous labelling studies have shown a non-linear incorporation of amino acids into tissue proteins, brush border membrane proteins and total proteins (explants + media) synthesized during the culture. A turnover of tissue proteins has been assumed from the release of labelled proteins into the culture media. The analysis of radioelectrophoregrams of brush border membrane proteins and proteins from the particulate fraction of media showed that the same brush border membrane proteins were synthesized in the tissue and released in the media all along the culture. 6. However, some quantitative differences have been found in the relative labelling between protein bands, suggesting that some proteins would be synthesized or released at different rates depending upon the duration of the culture.