Abstract
Selenite (SeO32-) was uptaken by the coccolithophorid, Emiliania huxleyi, as a source of selenium (Se), an analogous element of sulfur, to synthesize essential selenoproteins. In this research, we characterized kinetics of the selenite uptake systems under various conditions.
When the cells were grown under selenite-depleted conditions, Km values for the high-affinity transport system were decreased less than one-sixth in 3 days, whilst values of Vmax were almost constant. When 10 nM selenite was supplemented into the selenite deficient cells, the uptake activity was decreased in half in 24 h. These results suggested that high-affinity selenite transporter might be induced under the selenium deficient conditions.
Although sulfate did not affect the selenite uptake activity, the Km values of selenite uptake were increased to 3-fold of the control activity by the presence of sulfite or selenate. These results indicated that sulfite and selenate competitively inhibited the active transporter of selenite.
