The yeast Saccharomyces cerevisiae consumes mono- and disaccharides preferentially to any other carbon source. Since sugars do not freely permeate biological membranes, cellular uptake of these compounds requires the action of 'transporters'. The purpose of this review is to summarize the present knowledge on sugar transport in this organism. Yeast cells show two transporters for monosaccharides, the so-called glucose and galactose transporters that act by a facilitated diffusion mechanism. In the case of glucose transport, which also acts upon D-fructose and D-mannose, two components with high- and low-affinity constants have been identified kinetically. Activity of the high-affinity component is dependent on the presence of active kinases whereas activity of the low-affinity component is independent of the presence of these enzymes. Three genes, SNF3, HXT1 and HXT2, encode three different glucose transporters with a high affinity for the substrates and are repressed by high concentrations of glucose in the medium. Kinetic studies suggest that at least one additional gene exists that encodes a transporter with a low affinity and is expressed constitutively. The present view is that there are several additional transporters for glucose that have not yet been identified. Galactose transport has only one natural substrate, D-galactose, and is encoded by the gene GAL2. Expression of this gene is induced by galactose and repressed by glucose. Two transporters for disaccharides have been identified in S. cerevisiae: maltose and alpha-methylglucoside transporters. These transporters are H(+)-symports that depend on the electrochemical proton gradient and are independent of the ATP level. The gene that encodes the maltose transporter is clustered with the other two genes required for maltose utilization in a locus that is found repeated at different chromosomal locations. Its expression is induced by maltose and repressed by glucose. The rate of sugar uptake in yeast cells is controlled by changes in affinity of the corresponding transporters as well as by an irreversible inactivation that affects their Vmax. The mechanisms involved in these regulatory processes are unknown at present.

中文翻译：

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酿酒酵母中的糖运输。

酵母酿酒酵母比其他任何碳源优先消耗单糖和二糖。由于糖不能自由渗透生物膜，因此这些化合物的细胞吸收需要“转运蛋白”的作用。这篇综述的目的是总结目前关于这种生物中糖运输的知识。酵母细胞显示出两种单糖转运蛋白，即所谓的葡萄糖和半乳糖转运蛋白，它们通过促进的扩散机制起作用。在葡萄糖转运也作用于D-果糖和D-甘露糖的情况下，已经在动力学上鉴定了具有高亲和力常数和低亲和力常数的两个组分。高亲和力组分的活性取决于活性激酶的存在，而低亲和力组分的活性与这些酶的存在无关。三种基因SNF3，HXT1和HXT2编码三种对底物具有高亲和力的葡萄糖转运蛋白，并被培养基中高浓度的葡萄糖抑制。动力学研究表明存在至少一种另外的基因，该基因编码具有低亲和力的转运蛋白并组成性表达。目前的观点是，还有几种其他的葡萄糖转运蛋白尚未被发现。半乳糖转运只有一种天然底物D-半乳糖，由GAL2基因编码。该基因的表达由半乳糖诱导，并由葡萄糖抑制。在酿酒酵母中已经鉴定出两种二糖转运蛋白：麦芽糖和α-甲基葡糖苷转运蛋白。这些转运蛋白是H（+）-符号，它们取决于电化学质子梯度并且与ATP水平无关。编码麦芽糖转运蛋白的基因与在一个基因座利用麦芽糖所需的其他两个基因聚在一起，该基因座在不同的染色体位置重复出现。它的表达被麦芽糖诱导并被葡萄糖抑制。酵母细胞中糖的吸收速率受相应转运蛋白亲和力的变化以及影响其Vmax的不可逆失活的控制。目前尚不清楚这些调节过程涉及的机制。它的表达被麦芽糖诱导并被葡萄糖抑制。酵母细胞中糖的吸收速率受相应转运蛋白亲和力的变化以及影响其Vmax的不可逆失活的控制。目前尚不清楚这些调节过程涉及的机制。它的表达被麦芽糖诱导并被葡萄糖抑制。酵母细胞中糖的吸收速率受相应转运蛋白亲和力的变化以及影响其Vmax的不可逆失活的控制。目前尚不清楚这些调节过程涉及的机制。