Hatanaka M
J Cell Physiol. 1976 Dec;89(4):745-9. doi: 10.1002/jcp.1040890435.
Uptake of sugars into cells by a saturable process increased enormously during and after transformation, and uptake by a nonsaturable process increased significantly but less remarkably compared to controls. The drastic change of uptake rates, observed at around 5 x 10(-3) M sugar during and after transformation, emphasizes the significant observation that transition of the sugar uptake system from a saturable to a nonsaturable process occurs near the physiological concentration of D-glucose normally seen in animal blood. At concentrations below higher than 5 x 10(-3) M, where a saturable process is barely involved, nonsaturable uptakes of D-glucose, D-mannose, D-galactose, 2-deoxy-D-glucose and 3-O-methyl-D-glucose proceed tens to hundreds fold faster than the rate of simple diffusion of L-glucose. These findings suggest that nonsaturable uptake of the sugars known to be substrates for the saturable transport carrier system may not be a physical process or simple diffusion, as observed for L-glucose uptake. Rather, the nonsaturable uptake might be part of the total physiological process which, along with the saturable process, is controlled by a membrane-coordination mechanism. A plausible mechanism is discussed in which negative cooperativity of nutrient uptake, such as that found in bacteria, is involved.
在转化过程中及转化后，通过可饱和过程将糖摄入细胞的量大幅增加，而通过非饱和过程的摄入虽有显著增加，但与对照组相比增幅较小。在转化过程中及转化后，当糖浓度约为5×10⁻³ M时观察到的摄取速率的急剧变化，突出了一个重要发现：糖摄取系统从可饱和过程向非饱和过程的转变发生在动物血液中常见的D - 葡萄糖生理浓度附近。在高于或低于5×10⁻³ M的浓度下，几乎不存在可饱和过程，此时D - 葡萄糖、D - 甘露糖、D - 半乳糖、2 - 脱氧 - D - 葡萄糖和3 - O - 甲基 - D - 葡萄糖的非饱和摄取比L - 葡萄糖的简单扩散速率快数十至数百倍。这些发现表明，已知作为可饱和转运载体系统底物的糖的非饱和摄取可能不像L - 葡萄糖摄取那样是一个物理过程或简单扩散。相反，非饱和摄取可能是整个生理过程的一部分，该过程与可饱和过程一起受膜协调机制控制。文中讨论了一种合理的机制，其中涉及到如在细菌中发现的营养摄取的负协同作用。
