The capsular polysaccharides (CPS) of Campylobacter jejuni contain multiple heptose residues with variable stereochemical arrangements at C3–C6. The immediate precursor to all of these possible variations is currently believed to be GDP-d-glycero-α-d-manno-heptose. Oxidation of this substrate at C4 enables subsequent epimerization reactions at C3–C5 that can be coupled to the dehydration/reduction at C5/C6. However, the enzyme responsible for the critical oxidation of C4 from GDP-d-glycero-α-d-manno-heptose has remained elusive. The enzyme Cj1427 from C. jejuni NCTC 11168 was shown to catalyze the oxidation of GDP-d-glycero-α-d-manno-heptose to GDP-d-glycero-4-keto-α-d-lyxo-heptose in the presence of α-ketoglutarate using mass spectrometry and nuclear magnetic resonance spectroscopy. At pH 7.4, the apparent k_cat is 0.6 s^–1, with a value of k_cat/K_m of 1.0 × 10⁴ M^–1 s^–1 for GDP-d-glycero-α-d-manno-heptose. α-Ketoglutarate is required to recycle the tightly bound NADH nucleotide in the active site of Cj1427, which does not dissociate from the enzyme during catalysis.

中文翻译：

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Cj1427 的功能表征，这是一种独特的乒乓脱氢酶，负责空肠弯曲杆菌中 GDP-d-甘油-α-d-甘露-庚糖的氧化。

空肠弯曲杆菌的荚膜多糖 (CPS)含有多个庚糖残基，在 C3-C6 处具有可变的立体化学排列。目前认为所有这些可能变异的直接前体是GDP- d-甘油-α - d-甘露-庚糖。该底物在 C4 处的氧化使得 C3-C5 处的后续差向异构反应能够与 C5/C6 处的脱水/还原耦合。然而，负责从GDP - d-甘油-α- d-甘露-庚糖中关键氧化C4的酶仍然难以捉摸。来自空肠弯曲菌NCTC 11168的酶 Cj1427在存在的情况下可催化 GDP - d-甘油-α -d-甘露-庚糖氧化为 GDP - d-甘油-4-酮-α- d - lyxo-庚糖使用质谱法和核磁共振波谱法分析α-酮戊二酸。pH 7.4 时，表观k _cat为 0.6 s ^–1 ，对于 GDP- d -甘油-α- d -甘露-庚糖， k _cat / K _m值为1.0 × 10 ⁴ M ^–1 s ^–1。需要 α-酮戊二酸来回收 Cj1427 活性位点中紧密结合的 NADH 核苷酸，该核苷酸在催化过程中不会与酶解离。