Heller K B, Wilson T H
J Bacteriol. 1979 Nov;140(2):395-9. doi: 10.1128/jb.140.2.395-399.1979.
Several lines of evidence suggest that sucrose is transported by the lactose carrier of Escherichia coli. Entry of sucrose was monitored by an osmotic method which involves exposure of cells to a hyperosmotic solution of disaccharide (250 mM). Such cells shrink (optical density rises), and if the solute enters the cell, there is a return toward initial values (optical density falls). By this technique sucrose was found to enter cells at a rate approximately one third that of lactose. In addition, the entry of [14C]sucrose was followed by direct analysis of cell contents after separation of cells from the medium by centrifugation. Sucrose accumulated within the cell to a concentration 160% of that in the external medium. The addition of sucrose to an anaerobic suspension of cells resulted in a small alkalinization of the external medium. These data are consistent with the view that the lactose carrier can accumulate sucrose by a proton cotransport system. The carrier exhibits a very low affinity for the disaccharide (150 mM) but a moderately rapid Vmax.
多条证据表明，蔗糖是由大肠杆菌的乳糖载体转运的。通过一种渗透方法监测蔗糖的进入，该方法涉及将细胞暴露于二糖的高渗溶液（250 mM）中。此类细胞会收缩（光密度增加），如果溶质进入细胞，光密度会恢复到初始值（光密度下降）。通过该技术发现，蔗糖进入细胞的速率约为乳糖的三分之一。此外，在通过离心将细胞与培养基分离后，通过直接分析细胞内容物来追踪[14C]蔗糖的进入情况。蔗糖在细胞内积累的浓度是细胞外培养基中浓度的160%。向细胞的厌氧悬浮液中添加蔗糖会导致细胞外培养基出现轻微碱化。这些数据与乳糖载体可通过质子共转运系统积累蔗糖的观点一致。该载体对二糖的亲和力非常低（150 mM），但Vmax适中且较快。
