Determination of the apparent functional molecular mass of the hepatocellular sodium-dependent taurocholate transporter by radiation inactivation.
The apparent target size of the sodium-dependent taurocholate transporter in basolateral rat liver plasma membrane vesicles, showing overshooting taurocholate uptake in the presence of sodium was estimated by radiation inactivation. Radiation at -105 to -120 degrees C and 2.5 Mrad/min causes a dose-dependent monoexponential reduction of the overshoot of taurocholate uptake in the presence of sodium. In contrast, taurocholate transport in the absence of sodium and taurocholate permeation at 4 degrees C remained totally unaffected by the radiation dose, indicating that the passive permeability of the membrane towards taurocholate remained unaffected. Radiation inactivation by high-energy electrons provides information about the size of the functional unit of the transporter in situ. The target size determined represents the size of the radiation-sensitive mass which is compact enough for significant energy transfer to occur within all parts of the transport system. The minimal function molecular mass was determined to be 170 kDa for the sodium-dependent taurocholate transporter. To prove the validity of radiation inactivation data four internal standard enzymes were tested under identical conditions.
Institute of Pharmacology, Justus Liebig University, Giessen, F.R.G.
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R
Elsner
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Ziegler
D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D002462:Cell Membrane / Q000378:metabolism / Q000528:radiation effects / Q000648:ultrastructure; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008970:Molecular Weight; D051381:Rats; D013656:Taurocholic Acid / Q000378:metabolism*
D002352:Carrier Proteins; D013656:Taurocholic Acid