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首页> 外文期刊>Journal of bacteriology >Mechanism of Folate Transport in Lactobacillus casei: Evidence for a Component Shared with the Thiamine and Biotin Transport Systems
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Mechanism of Folate Transport in Lactobacillus casei: Evidence for a Component Shared with the Thiamine and Biotin Transport Systems

机译：叶酸干酪乳杆菌中叶酸运输的机制：与硫胺素和生物素运输系统共享的成分的证据。

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Lactobacillus casei cells have been shown previously to utilize two separate binding proteins for the transport of folate and thiamine. Folate transport, however, was found to be strongly inhibited by thiamine in spite of the fact that the folate-binding protein has no measurable affinity for thiamine. This inhibition, which did not fluctuate with intracellular adenosine triphosphate levels, occurred only in cells containing functional transport systems for both vitamins and was noncompetitive with folate but competitive with respect to the level of folate-binding protein. Folate uptake in cells containing optimally induced transport systems for both vitamins was inhibited by thiamine (1 to 10 μM) to a maximum of 45%; the latter value increased to 77% in cells that contained a progressively diminished folate transport system and a normal thiamine system. Cells preloaded with thiamine could transport folate at a normal rate, indicating that the inhibition resulted from the entry of thiamine rather than from its presence in the cell. In a similar fashion, folate (1 to 10 μM) did not interfere with the binding of thiamine to its transport protein, but inhibited thiamine transport (to a maximum of 25%). Competition also extended to biotin, whose transport was strongly inhibited (58% and 73%, respectively) by the simultaneous uptake of either folate or thiamine; biotin, however, had only a minimal effect on either folate or thiamine transport. The nicotinate transport system was unaffected by co-transport with folate, thiamine, or biotin. These results are consistent with the hypothesis that the folate, thiamine, and biotin transport systems of L. casei each function via a specific binding protein, and that they require, in addition, a common component present in limiting amounts per cell. The latter may be a protein required for the coupling of energy to these transport processes.
机译：以前已经证明干酪乳杆菌细胞利用两种单独的结合蛋白来运输叶酸和硫胺素。然而，尽管叶酸结合蛋白对硫胺素没有可测的亲和力，但发现叶酸胺能强烈抑制叶酸的转运。这种抑制作用不随细胞内三磷酸腺苷水平的变化而波动，仅在含有两种维生素功能转运系统的细胞中发生，与叶酸不竞争，但相对于叶酸结合蛋白的水平具有竞争性。硫胺素（1至10μM）将含有两种维生素的最佳诱导转运系统的细胞中的叶酸吸收抑制到最大45％;在含有逐渐减少的叶酸转运系统和正常硫胺素系统的细胞中，后者的值增加到77％。预装有硫胺素的细胞可以正常速度转运叶酸，表明抑制作用是由于硫胺素的进入而不是其在细胞中的存在而引起的。以类似的方式，叶酸（1至10μM）不会干扰硫胺素与其转运蛋白的结合，但会抑制硫胺素转运（最多25％）。竞争也扩展到生物素，同时摄取叶酸或硫胺素会严重抑制其运输（分别为58％和73％）;然而，生物素对叶酸或硫胺素的转运影响很小。烟酸转运系统不受与叶酸，硫胺素或生物素共同转运的影响。这些结果与“ L”的叶酸，硫胺素和生物素转运系统的假说相符。酪蛋白的每一种功能都通过特异性结合蛋白来实现，此外，它们还需要以每个细胞有限的量存在的共同成分。后者可能是能量耦合到这些转运过程所需的蛋白质。

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