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The Accumulation of Copper by Microvillar Vesicles Isolated from Human Placenta^1,2,

Centre for Research into Human Development, Department of Child Health, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY Scotland, U.K. ^* Interfacultair Reactor Instituut, Technische Universiteit Delft, Mekelweg 15 Delft, Holland

Copper uptake from copper-dihistidine complexes by microvillar vesicles from human placenta was studied. Uptake occurred in two phases: a rapid initial binding followed by approximately linear uptake to equilibrium at 5 min. The uptake showed temperature dependence, was saturable (apparent V_max 10.5 ± 1.6 nmol/(mg protein·4 min), apparent K_m of 0.6 ± 0.12 µmol/L) and decreased with increasing osmotic pressure, showing that the Cu uptake arose from accumulation within the vesicles and not from extravesicular binding or isotope exchange. Ceruloplasmin blocked uptake of ⁶⁴Cu from ⁶⁴Cu-dihistidine by the vesicles, with 50% inhibition achieved at a protein concentration of 5–10 µmol/L and a ⁶⁴Cu-dihistidine concentration of 1.5 µmol/L. The effect was specific, because glucose oxidase, a noncopper protein, increased apparent uptake by binding copper and in turn being bound to the nitrocellulose membranes used to separate vesicles from incubation medium. Adding increasing concentrations of histidine also decreased uptake. The data presented indicate that the placenta can accumulate copper from copper-dihistidine, that ceruloplasmin can interfere with uptake and that this system will be very valuable in elucidating the first stage in transfer of copper across the placenta.

KEY WORDS: • ceruloplasmin • placental transport • ⁶⁴Cu • copper transport • human placenta

¹ Supported by the Wellcome Trust and the British Council.

² Part of this work was presented by the University College London meeting of the Physiology Society, March 1991 [McArdle, H. J. & van den Berg, G. J. (1991) Uptake of copper by microvillar vesicles isolated from human placenta. J. Physiol. 438: 268P].

Manuscript received 17 April 1991. Revision accepted 30 December 1991.