Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA.
J Biol Chem. 2011 Mar 25;286(12):10193-200. doi: 10.1074/jbc.M110.194241. Epub 2011 Jan 27.
All mammals have 50-100 μM mannose in their blood. However, the source of the dynamic pool of mannose in blood is unknown. Most of it is thought to be derived from glucose in the cells. We studied mannose uptake and release by various cell types. Interestingly, our results show that mannose taken up by the cells through transporters is handled differently from the mannose released within the cells due to glycan processing of protein-bound oligosaccharides. Although more than 95% of incoming mannose is catabolized, most of the mannose released by intracellular processing is expelled from the cells as free mannose predominantly via a nocodazole-sensitive sugar transporter. Under physiological conditions, incoming mannose is more accessible to hexokinase, whereas mannose released within the cells is protected from HK and therefore has a different fate. Our data also suggest that generation of free mannose due to the processing of glycoconjugates composed of glucose-derived mannose and its efflux from the cells can account for most of the mannose found in blood and its steady state maintenance.
所有哺乳动物的血液中都含有 50-100 μM 的甘露糖。然而，血液中甘露糖动态池的来源尚不清楚。人们普遍认为，大部分甘露糖来自细胞内的葡萄糖。我们研究了各种细胞类型对甘露糖的摄取和释放。有趣的是，我们的结果表明，细胞通过转运蛋白摄取的甘露糖与由于蛋白结合寡糖的糖基化处理而在细胞内释放的甘露糖处理方式不同。尽管超过 95%的进入甘露糖被分解代谢，但由于糖基化处理，细胞内释放的大部分甘露糖主要通过无环鸟苷敏感的糖转运蛋白作为游离甘露糖被排出细胞。在生理条件下，进入的甘露糖更容易被己糖激酶利用，而细胞内释放的甘露糖则受到 HK 的保护，因此具有不同的命运。我们的数据还表明，由于由葡萄糖衍生的甘露糖组成的糖缀合物的加工以及从细胞内流出，会产生游离甘露糖，这可以解释血液中大部分甘露糖及其稳态维持的原因。
