Abstract
When chemically defined diets are required to provide optimal nutritional care in children, the choice of the most appropriate formula should be based on more detailed knowledge on absorption of protein hydrolytic products. Dipeptides can cross intact the intestinal brush border (b.b.)by way of selective transport systems; they can also be split at the b.b. membrane. While some peptides unhydrolyzed in the b.b. only follow the first pathway, for those which can be split in the b.b. the relative relevance of the two mechanisms is unknown. We have studied, in rabbit's intestinal mucosa, the uptake of Glycyl-Phenylalanine (GP) which both has affinity for the dipeptide transport process and is split at the b.b. GP(14CPhe) uptake has been measured in presence of large excesses either of Glycyl-Proline (Gly-Pro) or of Leucine, which are selective inhibitors of the peptide and the Phenylalanine transport systems, respectively. Under both conditions GP uptake follows Michaelis-Menten kinetics; in presence of Gly-Pro, GP(14CPhe) uptake shows kinetic constants similar to those reported for Phe influx, while in presence of Leucine the kinetic constants are similar to those reported for Gly-Pro influx. On the basis of the two sets of constants, it is concluded that GP is in part translocated by the peptide transport system, but at the concentrations at which it may occur in the intestinal lumen, the pathway ‘hydrolysis + amino acid transport’ is prevailing. In the latter pathway, the amino acid transport step seems to be the rate limiting one.
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Guandalini, S., Magazzu, G., Conti, A. et al. 152: A dual mechanism for transport of amino acid residues of dipeptides across the intestinal brush border. Pediatr Res 10, 895 (1976). https://doi.org/10.1203/00006450-197610000-00143
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DOI: https://doi.org/10.1203/00006450-197610000-00143