ABSTRACT
This chapter focuses on the transport of nitrogenous compounds by the ruminant gastrointestinal tract. Amino acids are transported by intestinal epithelium by simple diffusion, facilitated diffusion, and active transport processes. It is also apparent that the uptake of amino acids across the enterocyte into portal blood involves three steps. These include: transport from the intestinal lumen across the brush border membrane, diffusion through the enterocyte cytoplasm where metabolism and protein synthesis occur, and transport across the basal lateral membrane. Thus, the layers of the intestine should be stripped away when using in vitro techinques to study transport by enterocytes. The theory on peptide absorption is that peptides are transported from the lumen, hydrolyzed within the epithelial cell, and released into the bloodstream as free amino acid. While considering peptidases and peptides, it is appropriate to consider a specific peptidase called γ-glutamyl transferase.
