Kaplan J G, Tacreiter W
J Gen Physiol. 1966 Sep;50(1):9-24. doi: 10.1085/jgp.50.1.9.
There are two distinct components of the system which limits the rate at which intact cells of S. cerevisiae C hydrolyze external beta-glucosides; one component requires metabolic energy and the other is stereospecific for beta-glucosides. The stereospecific component is localized at the cell membrane, as shown by its sensitivity to heavy metal inhibitors which did not penetrate the cell under the conditions used. It was shown that cellobiose-grown cells were able to remove cellobiose from the medium in which they were incubated, and that the cellobiose uptake system was identical to that which limits the patent beta-glucosidase activity. In order to test the hypothesis that the system in question was a transport system, for beta-glucosides the ability of cellobiose-grown cells to take up (14)C-labeled methyl-beta-glucoside (MBG) was studied. The induced cells were able to take up MBG-(14)C and the label could be partially chased out by cold MBG and cellobiose; glucose-grown cells could not incorporate label. However, induced cells could not take up label when incubated with (14)C-MBG, thus excluding the hypothesis of transport of intact beta-glucosides. It was concluded that the stereospecific membrane component was actually a beta-glucosidase, coupled to an energy-dependent transport system for the glucose moiety; the function of the latter was rate-limiting in the over-all activity of the entire system.
该系统有两个不同的组成部分，它们限制了酿酒酵母C完整细胞水解外源性β-葡萄糖苷的速率；一个组成部分需要代谢能量，另一个对β-葡萄糖苷具有立体特异性。立体特异性组成部分定位于细胞膜，这可通过其对重金属抑制剂的敏感性得以证明，在所用条件下这些抑制剂无法穿透细胞。结果表明，以纤维二糖培养的细胞能够从其孵育的培养基中去除纤维二糖，并且纤维二糖摄取系统与限制专利β-葡萄糖苷酶活性的系统相同。为了检验所讨论的系统是一种转运系统这一假设，针对β-葡萄糖苷，研究了以纤维二糖培养的细胞摄取（14）C标记的甲基-β-葡萄糖苷（MBG）的能力。诱导细胞能够摄取MBG-（14）C，并且标记物可被冷的MBG和纤维二糖部分逐出；以葡萄糖培养的细胞不能掺入标记物。然而，诱导细胞与（14）C-MBG一起孵育时不能摄取标记物，因此排除了完整β-葡萄糖苷转运的假设。得出的结论是，立体特异性膜组成部分实际上是一种β-葡萄糖苷酶，与葡萄糖部分的能量依赖性转运系统偶联；后者的功能在整个系统的总体活性中起限速作用。
