TY - JOUR
T1 - Sodium-dependent high-affinity binding of carnitine to human placental brush border membranes
AU - Roque, Arlene S.
AU - Prasad, Puttur D.
AU - Bhatia, Jatinder S.
AU - Leibach, Frederick H.
AU - Ganapathy, Vadivel
N1 - Funding Information:
This work was supported in part by National Institutes of Health Grant HD 24451 (V.G.) and Wyeth-Lederle Neonatology Research Grant (A.S.R.). The authors thank Sarah Taylor for expert secretarial assistance.
PY - 1996/7/25
Y1 - 1996/7/25
N2 - 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 μM. 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 possess neither Na+ gradient-driven carnitine transport nor Na+-dependent carnitine binding.
AB - 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 μM. 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 possess neither Na+ gradient-driven carnitine transport nor Na+-dependent carnitine binding.
KW - Brush-border membrane
KW - Carnitine
KW - High-affinity binding
KW - Human placenta
KW - Sodium ion dependence
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U2 - 10.1016/0005-2736(96)00068-5
DO - 10.1016/0005-2736(96)00068-5
M3 - Article
C2 - 8703983
AN - SCOPUS:0030601156
SN - 0005-2736
VL - 1282
SP - 274
EP - 282
JO - Biochimica et Biophysica Acta - Biomembranes
JF - Biochimica et Biophysica Acta - Biomembranes
IS - 2
ER -