Schloss J V, Lorimer G H
J Biol Chem. 1982 May 10;257(9):4691-4.
The carboxylation of ribulosebisphosphate involves a 6-carbon reaction-intermediate, 2-carboxy-3-keto-D-arabinitol 1,5-bisphosphate. This labile intermediate, radiolabeled with 14CO2, was reduced (and thereby stabilized) with NaB[3H4]. This yielded a doubly labeled mixture with the chromatographic properties of 2-carboxy- and 4-carboxy-D-arabinitol 1,5-bisphosphate. These products (as their respective gamma-lactones) were chromatographically resolved from the gamma-lactones of 2-carboxy-D-ribitol and 2-carboxy-D-xylitol 1,5-bisphosphate, the other possible reduction products to be considered. Reduction of the 6-carbon reaction-intermediate by NaBH4 required prior denaturation of the enzyme. Of various denaturants tested, only acid was rapid enough to give good yields of the carboxypentitol bisphosphates. The reduction products of the reaction-intermediate inhibited the carboxylase stoichiometrically. In contrast to 2-carboxyribitol and 2-carboxyxylitol bisphosphate, 2-carboxy- and 4-carboxyarabinitol bisphosphate are exceptionally potent, essentially irreversible, slow-binding inhibitors of ribulosebisphosphate carboxylase.
核酮糖二磷酸的羧化作用涉及一种六碳反应中间体，即2-羧基-3-酮-D-阿拉伯糖醇1,5-二磷酸。这种不稳定的中间体用¹⁴CO₂进行放射性标记后，用硼氢化钠[³H₄]进行还原（从而使其稳定）。这产生了一种双重标记的混合物，具有2-羧基-D-阿拉伯糖醇1,5-二磷酸和4-羧基-D-阿拉伯糖醇1,5-二磷酸的色谱性质。这些产物（作为它们各自的γ-内酯）通过色谱法与2-羧基-D-核糖醇和2-羧基-D-木糖醇1,5-二磷酸的γ-内酯分离，这是另外两种可能需要考虑的还原产物。用硼氢化钠还原六碳反应中间体需要酶先进行变性。在测试的各种变性剂中，只有酸的作用速度足够快，能产生高产率的羧基戊糖醇二磷酸。反应中间体的还原产物对羧化酶有化学计量的抑制作用。与2-羧基核糖醇和2-羧基木糖醇二磷酸不同，2-羧基-D-阿拉伯糖醇1,5-二磷酸和4-羧基-D-阿拉伯糖醇1,5-二磷酸是核酮糖二磷酸羧化酶异常有效的、基本上不可逆的、慢结合抑制剂。
