29 AAs - Absorption and Cellular Uptake

29 AAs - Absorption and Cellular Uptake - Amino Acids and...

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Amino Acids and Proteins: Intestinal Absorption and Cellular Uptake HNFE 3025 Fall 2009
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Absorption can occur along the entire length of the small intestine Most absorption is in the proximal small intestine There are multiple energy-dependent transport systems overlapping specificity for amino acids Na + -dependent and Na + -independent amino acid transport Free AAs and small peptides are absorbed using different transport systems Amino Acid Absorption
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Amino Acid Absorption enterocyte Brush border (apical) membrane Intestinal lumen Basolateral membrane capillary AA AA AA AA transporter AA transporter ECF paracellular absorption
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Dependence on Na + concentration gradient – [Na + ] lumen >> [Na + ] in enterocyte Redundancy More than one transporter can transport a particular AA Competition AA will compete for a transporter they have in common Apical Enterocyte Amino Acid Transporters 4 Table 6-4, p. 192
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AA Na + Basolateral membrane Generally, the binding of Na + increases the affinity of the transporter for the AA A conformational change internalizes the AA and Na + They are both released into the cytosol and the transporter returns to its original conformation To maintain the balance of electrolytes, the Na + /K + ATPase must be active Na + -dependent Brush Border Amino Acid Transport 5 Na + AA Na + AA Na + AA Na + AA K + K + Na + Na + /K + ATPase Na + Lumen of the small intestine Cytosol of an enterocyte Brush Border (apical) membrane
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All AA are not absorbed equally Increased hydrocarbon mass increases affinity for the AA Neutral AAs have greater affinity than charged AAs Essential AAs are absorbed faster than nonessential AAs Asp and Glu are the slowest to be absorbed AA Absorption Rates 6 isoleucine (Ile) alanine (Ala) Which of these AAs will have a greater affinity for the carrier?
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Peptide transport into the enterocytes uses different transporters than AAs. Several systems,
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29 AAs - Absorption and Cellular Uptake - Amino Acids and...

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