In eukaryotes, the D-enantiomer of arabinose (D-Ara) is an intermediate in the biosynthesis of D-erythroascorbate in yeast and fungi and in the biosynthesis of the nucleotide sugar GDP-α-D-arabino (GDP-D-Ara) and complex α-D-Ara–containing surface glycoconjugates in certain trypanosomatid parasites. Whereas the biosynthesis of D-Ara in prokaryotes is well understood, the route from D-glucose (D-Glc) to D-Ara in eukaryotes is unknown. In this paper, we study the conversion of D-Glc to D-Ara in the trypanosomatid using positionally labeled [C]-D-Glc and [C]-D-ribose ([C]-D-Rib) precursors and a novel derivatization and gas chromatography-mass spectrometry procedure applied to a terminal metabolite, lipoarabinogalactan. These data implicate the both arms of pentose phosphate pathway and a likely role for D-ribulose-5-phosphate (D-Ru-5P) isomerization to D-Ara-5P. We tested all putative sugar and polyol phosphate isomerase genes for their ability to complement a D-Ara-5P isomerase-deficient mutant of and found that one, the glutamine fructose-6-phosphate aminotransferase (GFAT) of glucosamine biosynthesis, was able to rescue the mutant. We also found that GFAT genes of other trypanosomatid parasites, and those of yeast and human origin, could complement the mutant. Finally, we demonstrated biochemically that recombinant human GFAT can isomerize D-Ru-5P to D-Ara5P. From these data, we postulate a general eukaryotic pathway from D-Glc to D-Ara and discuss its possible significance. With respect to , we propose that D-Ara is used not only for the synthesis of GDP-D-Ara and complex surface glycoconjugates but also in the synthesis of D-erythroascorbate.

中文翻译：

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真核生物中从 D-葡萄糖到 D-阿拉伯糖的拟议途径


在真核生物中，阿拉伯糖的 D-对映体 (D-Ara) 是酵母和真菌中 D-赤式抗坏血酸生物合成以及核苷酸糖 GDP-α-D-阿拉伯糖 (GDP-D-Ara) 生物合成的中间体某些锥虫寄生虫中含有复杂的 α-D-Ara 表面糖缀合物。虽然原核生物中 D-Ara 的生物合成已被充分了解，但真核生物中从 D-葡萄糖 (D-Glc) 到 D-Ara 的途径尚不清楚。在本文中，我们使用位置标记的 [C]-D-Glc 和 [C]-D-核糖 ([C]-D-Rib) 前体和一种新的方法，研究了锥虫中 D-Glc 向 D-Ara 的转化。衍生化和气相色谱-质谱法应用于末端代谢物脂阿拉伯半乳聚糖。这些数据暗示了磷酸戊糖途径的两个分支以及 D-核酮糖-5-磷酸 (D-Ru-5P) 异构化为 D-Ara-5P 的可能作用。我们测试了所有假定的糖和多元醇磷酸异构酶基因补充 D-Ara-5P 异构酶缺陷突变体的能力，发现其中一种，即葡萄糖胺生物合成的谷氨酰胺果糖-6-磷酸转氨酶 (GFAT)，能够挽救突变体。我们还发现其他锥虫寄生虫以及酵母和人类来源的 GFAT 基因可以补充突变体。最后，我们通过生化证明重组人GFAT可以将D-Ru-5P异构化为D-Ara5P。根据这些数据，我们假设了从 D-Glc 到 D-Ara 的一般真核途径，并讨论了其可能的意义。关于 ，我们建议 D-Ara 不仅用于 GDP-D-Ara 和复杂表面糖缀合物的合成，而且还用于 D-赤式抗坏血酸的合成。