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Transport of thiamine by brush‐border membrane vesicles from rat small intestine.
Author(s) -
Casirola D,
Ferrari G,
Gastaldi G,
Patrini C,
Rindi G
Publication year - 1988
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1988.sp017045
Subject(s) - brush border , thiamine , vesicle , small intestine , chemistry , brush , thiamine deficiency , membrane , biophysics , biochemistry , biology , materials science , composite material
1. Microvillous vesicles obtained by a Ca2+ precipitation method from the intestine of adult Wistar albino rats were incubated at 25 degrees C with [35S]‐ or [3H]thiamine of high specific activity. 2. The time course of thiamine uptake was not influenced by the presence of Na+ or K+ nor by the absence of alkaline cations in the incubation medium. 3. At concentrations below 1.25 microM, thiamine was taken up mainly by a saturable mechanism with apparent Km = 0.8 microM and Vmax = 0.35 pmol mg protein‐1 4 s‐1. At higher concentrations, a non‐saturable uptake mechanism prevailed. 4. The thiamine taken up was transferred to the intravesicular space. No thiamine phosphoesters could be detected in the vesicles. 5. The vesicular transport of thiamine was inhibited competitively by several thiamine derivatives and structural analogues, including: cold thiamine; thiamine monophosphate (inhibition constant, Ki = 33 microM); pyrithiamine (Ki = 1.7 microM); 2'‐ethylthiamine (Ki = 27 microM); 5‐chloroethylthiamine (Ki = 70 microM): Amprolium (Ki = 55 microM); 4'‐oxythiamine (Ki = 510 microM).