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Characterization of the unidirectional transport of carnitine catalyzed by the reconstituted carnitine carrier from rat liver mitochondria.

Authors
  • Indiveri, C
  • Tonazzi, A
  • Palmieri, F
Type
Published Article
Journal
Biochimica et Biophysica Acta
Publisher
Elsevier
Publication Date
Oct 14, 1991
Volume
1069
Issue
1
Pages
110–116
Identifiers
PMID: 1932043
Source
Medline
License
Unknown

Abstract

The carnitine carrier from rat liver mitochondria was purified by chromatography on hydroxyapatite and celite and reconstituted in egg yolk phospholipid vesicles by adsorbing the detergent on polystyrene beads. In the reconstituted system, in addition to the carnitine/carnitine exchange, the purified protein catalyzed a uni-directional transport (uniport) of carnitine measured as uptake into unloaded proteoliposomes as well as efflux from prelabelled proteoliposomes. In both cases the reaction followed a first-order kinetics with a rate constant of 0.023-0.026 min-1. Besides carnitine, also acylcarnitines were transported in the uniport mode. N-Ethylmaleimide inhibited the uni-directional transport of carnitine completely. The uniport of carnitine is not influenced by the delta pH and the electric gradient across the membrane. The activation energy for uniport was 115 kJ/mol and the half-saturation constant on the external side of the proteoliposomes was 0.53 mM. The maximal rate of the uniport at 25 degrees C was 0.2 mumol/min per mg protein, i.e. about 10 times lower than that of the reconstituted carnitine transport in exchange mode.

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