HIGH-AFFINITY MALTOSE TREHALOSE TRANSPORT-SYSTEM IN THE HYPERTHERMOPHILIC ARCHAEON THERMOCOCCUS-LITORALIS/

The hyperthermophilic marine archaeon Thermococcus litoralis exhibits high-affinity transport activity for maltose and trehalose at 85 degre es C. The K-m for maltose transport was 22 nM, and that for trehalose was 17 nM. In cells that had been grown on peptone plus yeast extract, the V-max for maltose uptake ranged from 3.2 to 7.5 nmol/min/mg of pr otein in different cell cultures. Cells grown in peptone without yeast extract did not show significant maltose or trehalose uptake. We foun d that the compound in yeast extract responsible for the induction of the maltose and trehalose transport system was trehalose. [C-14] malto se uptake at 100 nM was not significantly inhibited by glucose, sucros e, or maltotriose at a 100 mu M concentration but was completely inhib ited by trehalose and maltose. The inhibitor constant, K-i, of trehalo se for inhibiting maltose uptake was 21 nM. In contrast, the ability o f maltose to inhibit the uptake of trehalose was not equally strong. W ith 20 nM [C-14]trehalose as the substrate, a 10-fold excess of maltos e was necessary to inhibit uptake to 50%. However, full inhibition was observed at 2 mu M maltose. The detergent-solubilized membranes of tr ehalose-induced cells contained a high-affinity binding protein for ma ltose and trehalose, with an M(r) of 48,000, that exhibited the same s ubstrate specificity as the transport system found in whole cells. We conclude that maltose and trehalose are transported by the same high-a ffinity membrane-associated system. This represents the first report o n sugar transport in any hyperthermophilic archaeon.