Carrier-mediated transport of thiamine in baker's yeast

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Abstract 1. 1. The characteristics of a system of [ 14 C]thiamine uptake were investigated in baker's yeast ( Saccharomyces cerevisaie ). 2. 2. [ 14 C]Thiamine uptake by the system was found to be an energy- and temperature-dependent process which has an optimal pH at 4.5. 3. 3. Most of [ 14 C]thiamine taken up existed intracellularly in free form, which accumulated against a large concentration difference. 4. 4. The apparent K m for [ 14 C]thiamine uptake was 1.8·10 −7 M, and the uptake of labeled thiamine was inhibited by several thiamine analogues, except for oxythiamine. 5. 5. Short-chain fatty acids (C 2 –C 6 ) strongly inbibited [ 14 C]thiamine uptake. 6. 6. Caproate, which has a most pronounced inhibitory effect on [ 14 C]thiamine uptake, brought about the exit of [ 14 C]thiamine taken up. 7. 7. Pyrithiamine inhibited significantly [ 14 C]thiamine exit caused by caproate, whereas oxythiamine did not. 8. 8. It was discussed whether the uptake of thiamine in baker's yeast occurs by a carrier-mediated active process.

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