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Protein and amino acids
Published in Geoffrey P. Webb, Nutrition, 2019
Also located on the surface of the small intestine are dipeptidases and tripeptidases, which break down dipeptides and tripeptides. Dipeptidases and tripeptidases within the cells complete the digestion of any dipeptides and tripeptides that are absorbed intact into the intestinal cells.
Macromolecular Absorption From The Digestive Tract In Young Vertebrates
Published in Károly Baintner, Intestinal Absorption of Macromolecules and Immune Transmission from Mother to Young, 2019
The few data available indicate that oligopeptidases show fairly high activities in the brush border of the enterocytes of newborn animals. In the piglet, l-Ala-l-Glu and Gly-l-Leu dipeptidase activities (apparently activities of the same enzyme) show peak values in the perinatal days, then gradually decrease to the adult level. The l-Ala-l-Pro dipeptidase activity already approximates the adult level at birth.842
Introduction
Published in Shayne C. Gad, Toxicology of the Gastrointestinal Tract, 2018
Protein digestion starts in the stomach, where proteins are fragmented into peptides by the action of pepsin. Enzymes in pancreatic juice—trypsin, chymotrypsin, carboxypeptidase, and elastase—continue to break down proteins into peptides. Although all these enzymes convert whole proteins into peptides, their actions differ somewhat because each splits peptide bonds between different amino acids. Trypsin, chymotrypsin, and elastase all cleave the peptide bond between a specific amino acid and its neighbor; carboxypeptidase breaks the peptide bond that attaches the terminal amino acid to the carboxyl (acid) end of the peptide. Protein digestion is completed by two peptidases in the brush border: aminopeptidase and dipeptidase. Aminopeptidase acts on peptides by breaking the peptide bond that attaches the terminal amino acid to the amino end of the peptide. Dipeptidase splits dipeptides into single amino acids.
Inhibition of human erythrocyte glutathione S-transferase by some flavonoid derivatives
Published in Toxin Reviews, 2018
Detoxification is vital in the defense system of living organisms. More specifically, glutathione transferase (GST; EC 2.5.1.18) plays an important role in detoxification. The conjugation of γ-glutamyl-cysteinyl-glycine (GSH) with electrophilic compounds such as drugs, toxins, and carcinogens is catalyzed by GST. The conjugation of GSH with electrophilic xenobiotics produces less toxic and more water soluble derivatives (Tew and Townsend 2012). GSH conjugates can be eliminated via bile or the kidney. After the transfer of GSH conjugates to the kidneys, γ-glutamyl transpeptidase cleaves the γ-glutamyl moiety. Next, dipeptidase separates glycine and cysteine N-acetylation excretes as a mercapturic acid. The transport of glutathione conjugates is provided by ATP binding cassette (ABC) transporters. The membrane-bound GS-X pump, which is a member of the ABC transporter family, takes a part in the elimination of anticancer drugs complexes with GSH or GSH conjugates (Board and Menon 2013).
The challenges of oral drug delivery via nanocarriers
Published in Drug Delivery, 2018
Jonas Reinholz, Katharina Landfester, Volker Mailänder
However, the oral dosage form also has several drawbacks. Before the orally applied drug is able to reach its target, in most instances it needs to overcome multiple compartments of the human body, which is challenging for a broad spectrum of pharmaceuticals, especially for protein- or peptide-based ones. In general, the first major challenge for the drug after ingestion is surviving the harsh acidic pH value in the stomach. In addition, the proteases pepsin and cathepsin start to digest proteins into peptides. Once the drug surpasses the stomach and enters the small intestine via the duodenum, it faces the major enzymatic digestion machinery of the human body. Oligosaccharides and maltose are degraded into glucose, fructose, galactose, and mannose via sucrase, maltase, and lactase. Lipids are cleaved into glycerol and fatty acids via the pancreatic triacylglycerol lipase and carboxyl ester lipase. Peptides are digested into amino acids via trypsin, chymotrypsin, carboxypeptidase, dipeptidase, and aminopeptidase.
The mercapturic acid pathway
Published in Critical Reviews in Toxicology, 2019
Patrick E. Hanna, M. W. Anders
NAT8 activity is found, along with GGT and dipeptidase activities in the outer stripe region of the medulla of the rat kidney, which contains proximal tubular cells (Hughey et al. 1978). Immunohistochemical studies show that NAT8 is highly expressed in the proximal tubular cells of the inner and outer cortices of human kidney (Chambers et al. 2010, Supplementary Figures 4 and 5).