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Selective sites for polyamine binding to rabbit intestinal brush-border membranes
P Brachet1, J E Long, E R Siedel
1Unité de Nutrition Cellulaire et Moléculaire, Institut National de la Recherche Agronomique, Clermont-Ferrand-Theix, France. brachet@clermont.inra.fr
Biochemical Pharmacology
|October 8, 1998
Summary
Researchers identified distinct polyamine binding sites in rabbit intestinal membranes, a crucial step toward discovering intestinal polyamine transporters. These sites show varied affinities and ligand selectivity, suggesting complex transport mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Gastroenterology
Background:
- Intestinal polyamine transporters are currently unidentified.
- Understanding these transporters is crucial for comprehending polyamine absorption and regulation in the gut.
Purpose of the Study:
- To characterize specific polyamine binding sites in rabbit intestinal brush-border membranes (IBBM).
- To lay the groundwork for the identification of novel polyamine transporters.
Main Methods:
- Investigated [3H]putrescine (PUT), [3H]spermidine (SPD), and [14C]spermine (SPM) binding to IBBM at 4°C.
- Analyzed binding kinetics, including association, dissociation, and inhibition using specific ligands and competitors.
- Determined dissociation equilibrium constants (Kd) and site densities (Bmax) for identified binding sites.
Main Results:
- Identified a single class of putrescine binding sites (puT) with Kd = 3.8 μM and Bmax = 58 pmol/mg protein.
- Discovered one class of spermidine binding sites (spD) with lower affinity (Kd = 106 μM) and higher abundance (Bmax = 1240 pmol/mg protein).
- Characterized two classes of spermine binding sites (spM1, spM2) with distinct affinities (Kd = 2.5, 31.4 μM) and abundances (Bmax = 467, 1617 pmol/mg protein).
Conclusions:
- The intestinal brush-border membrane possesses at least three distinct polyamine binding sites with differential ligand selectivity.
- The identified puT site may be linked to the known intestinal putrescine uptake system.
- These findings provide essential insights into the molecular mechanisms of intestinal polyamine transport.