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Sodium-dependent high-affinity binding of carnitine to human placental brush border membranes.
- Source :
-
Biochimica et biophysica acta [Biochim Biophys Acta] 1996 Jul 25; Vol. 1282 (2), pp. 274-82. - Publication Year :
- 1996
-
Abstract
- The interaction of carnitine with human placental brush-border membrane vesicles was investigated. Carnitine was found to associate with the membrane vesicles in a Na(+)-dependent manner. The time course of this association did not exhibit an overshoot, which is typical of a Na+ gradient-driven transport process. The absolute requirement for Na+ was noticeable whether the association of carnitine with the vesicles was measured with a short time incubation or under equilibrium conditions, indicating Na(+)-dependent binding of carnitine to the human placental brush-border membranes. The binding was saturable and was of a high-affinity type with a dissociation constant of 1.37 +/- 0.03 microM. Anions had little or no influence on the binding process. The binding process was specific for carnitine and its acyl derivatives. Betaine also competed for the binding process, but other structurally related compounds did not. Kinetic analyses revealed that Na+ increased the affinity of the binding process for carnitine and the Na+/carnitine coupling ratio for the binding process was 1. The dissociation constant for the interaction of Na+ with the binding of carnitine was 24 +/- 4 mM. This constitutes the first report on the identification of Na(+)-dependent high-affinity carnitine binding in the plasma membrane of a mammalian cell. Studies with purified rat renal brush-border membrane vesicles demonstrated the presence of Na+ gradient-driven carnitine transport but no Na(+)-dependent carnitine binding in these membrane vesicles. In contrast, purified intestinal brush-border membrane vesicles posses neither Na+ gradient-driven carnitine transport nor Na(+)-dependent carnitine binding.
- Subjects :
- Anions
Betaine metabolism
Binding, Competitive
Biological Transport
Cations
Female
Humans
Intestines ultrastructure
Kidney ultrastructure
Kinetics
Liposomes metabolism
Potassium Chloride pharmacology
Pregnancy
Carnitine metabolism
Microvilli metabolism
Placenta ultrastructure
Sodium pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 0006-3002
- Volume :
- 1282
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- Biochimica et biophysica acta
- Publication Type :
- Academic Journal
- Accession number :
- 8703983
- Full Text :
- https://doi.org/10.1016/0005-2736(96)00068-5