Pierce J, Tolbert N E, Barker R
Biochemistry. 1980 Mar 4;19(5):934-42. doi: 10.1021/bi00546a018.
2-C-Carboxy-D-ribitol 1,5-bisphosphate and 2-C-carboxy-D-arabinitol 1,5-bisphosphate have been synthesized, purified, and characterized. In the presence of Mg2+, 2-C-carboxy-D-arabinitol 1,5-bisphosphate binds to ribulose-1,5-bisphosphate carboxylase/oxygenase by a two-step mechanism. The first, rapid step is similar to the binding of ribulose 1,5-bisphosphate or its structural analogues. The second step is a slower process (k = 0.04 s-1) and accounts for the tighter binding of 2-C-carboxy-D-arabinitol 1,5-bisphosphate (Kd less than or approximately to 10(-11) M) than of 2-C-carboxy-D-ribitol 1,5-bisphosphate (Kd = 1.5 X 10(6) M). Both carboxypentitol bisphosphates exhibit competitive inhibition with respect to ribulose 1,5-bisphosphate. 2-C-(Hydroxymethyl)-D-ribitol 1,5-bisphosphate and 2-C-(hydroxymethyl)-D-arabinitol 1,5-bisphosphate were also synthesized; both are competitive inhibitors with respect to ribulose 1,5-bisphosphate with Ki = 8.0 X 10(-5) M and Ki = 5.0 X 10(-6) M, respectively. Thus, the carboxyl group of 2-C-carboxy-D-arabinitol 1,5-bisphosphate is necessary for maximal interaction with the enzyme. Additionally, Mg2+ is essential for the tight binding of 2-C-carboxy-D-arabinitol 1,5-bisophsphate. A model for catalysis of ribulose 1,5-bisphosphate carboxylation is discussed which includes a functional role for Mg2+ in the stabilization of the intermediate 2-C-carboxy-3-keto-D-arabinitol 1,5-bisphosphate. Mechanistic implications that arise from the stereochemistry of this intermediate are also discussed.
2-C-羧基-D-核糖醇1,5-二磷酸酯和2-C-羧基-D-阿拉伯糖醇1,5-二磷酸酯已被合成、纯化和表征。在Mg2+存在下，2-C-羧基-D-阿拉伯糖醇1,5-二磷酸酯通过两步机制与核酮糖-1,5-二磷酸羧化酶/加氧酶结合。第一步是快速步骤，类似于核酮糖1,5-二磷酸酯或其结构类似物的结合。第二步是较慢的过程（k = 0.04 s-1），这解释了2-C-羧基-D-阿拉伯糖醇1,5-二磷酸酯（Kd小于或约为10(-11) M）比2-C-羧基-D-核糖醇1,5-二磷酸酯（Kd = 1.5×10(6) M）结合更紧密的原因。两种羧基戊糖醇二磷酸酯对核酮糖1,5-二磷酸酯均表现出竞争性抑制作用。还合成了2-C-(羟甲基)-D-核糖醇1,5-二磷酸酯和2-C-(羟甲基)-D-阿拉伯糖醇1,5-二磷酸酯；它们对核酮糖1,5-二磷酸酯均为竞争性抑制剂，Ki分别为8.0×10(-5) M和5.0×10(-6) M。因此，2-C-羧基-D-阿拉伯糖醇1,5-二磷酸酯的羧基对于与该酶的最大相互作用是必需的。此外，Mg2+对于2-C-羧基-D-阿拉伯糖醇1,5-二磷酸酯的紧密结合至关重要。讨论了核酮糖1,5-二磷酸羧化催化的模型，其中包括Mg2+在稳定中间体2-C-羧基-3-酮-D-阿拉伯糖醇1,5-二磷酸酯中的功能作用。还讨论了由该中间体的立体化学产生的机制含义。
