Energetics of reserpine binding and occlusion by the chromaffin granule biogenic amine transporter.
The energetics of reserpine binding to the bovine adrenal biogenic amine transporter suggest that H+ ion translocation converts the transporter to a form which binds reserpine essentially irreversibly. Reserpine binding to bovine adrenal chromaffin granule membrane vesicles is accelerated by generation of a transmembrane pH difference (delta pH) (interior acid) or electrical potential (delta psi) (interior positive). Both components of the electrochemical H+ potential (delta mu H+) must be dissipated to block reserpine binding, and generation of either one stimulates the binding rate. Reserpine binding is less dependent than amine transport on the delta pH, suggesting that translocation of fewer H+ ions is required to expose the high-affinity site than are required for net transport. Bound reserpine dissociates very slowly, if at all, from the transporter. Binding is stable to 1% cholate, 1.5% Triton X-100, 1 M SCN-, and 8 M urea, but sodium dodecyl sulfate (0.035%) and high temperatures (100 degrees C) released bound reserpine, indicating that binding is noncovalent. The results raise the possibility that the transporter, by translocating one H+ ion outward down its concentration gradient, is converted to a form that can either transport a neutral substrate molecule inward or occlude reserpine in a dead-end complex.
Rudnick
G
G
Department of Molecular Biology, Hadassah Medical School, Hebrew University of Jerusalem, Israel.
Steiner-Mordoch
S S
SS
Fishkes
H
H
Stern-Bach
Y
Y
Schuldiner
S
S
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000645:Ammonium Sulfate / Q000494:pharmacology; D001665:Binding Sites; D001679:Biogenic Amines / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D002837:Chromaffin Granules / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008564:Membrane Potentials; D012110:Reserpine / Q000378:metabolism*; D013816:Thermodynamics; D013861:Thiocyanates / Q000494:pharmacology; D013997:Time Factors; D014508:Urea / Q000494:pharmacology
D001679:Biogenic Amines; D002352:Carrier Proteins; D002712:Chlorides; D003902:Detergents; D007476:Ionophores; D008024:Ligands; D013861:Thiocyanates; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012110:Reserpine; D014508:Urea; D000251:Adenosine Triphosphatases; D000645:Ammonium Sulfate