Cadet F, Meunier J C, Ferté N
Eur J Biochem. 1987 Jan 15;162(2):393-8. doi: 10.1111/j.1432-1033.1987.tb10614.x.
This report describes the effects of pH and fructose 2,6-bisphosphate (an analog of fructose 1,6-bisphosphate) on the activity of oxidized and reduced fructose-1,6-bisphosphatase from spinach chloroplasts. Studies were carried out with either fructose 1,6-bisphosphate, the usual substrate, or sedoheptulose 1,7-bisphosphate, an alternative substrate. The reduction of the oxidized enzyme is achieved by a thiol/disulfide interchange. The pK values relative to each redox form for the same substrate (either fructose 1,6-bisphosphate or sedoheptulose 1,7-bisphosphate) are identical, suggesting the same site for both substrates on the active molecule. The finding that the analog (fructose 2,6-bisphosphate) behaves like a competitive inhibitor for both substrates also favours this hypothesis. The inhibitory effect of this sugar is more important when the enzyme is reduced than when it is oxidized. The shift in the optimum pH observed when [Mg2+] was raised is interpreted as a conformational change of oxidized enzyme demonstrated by a change in fluorescence. The reduced and oxidized forms have the same theoretical rates relative to both substrates, but the reduced form has an observed Vmax which is 60% of the theoretical Vmax while that of the oxidized form is only 37% of the theoretical Vmax. The reduced enzyme appears more efficient than the oxidized one in catalysis.
本报告描述了pH值和果糖2,6 - 二磷酸（果糖1,6 - 二磷酸的类似物）对菠菜叶绿体中氧化型和还原型果糖-1,6 - 二磷酸酶活性的影响。研究使用了通常的底物果糖1,6 - 二磷酸或替代底物景天庚酮糖1,7 - 二磷酸进行。氧化型酶的还原通过硫醇/二硫键交换实现。对于相同底物（果糖1,6 - 二磷酸或景天庚酮糖1,7 - 二磷酸），相对于每种氧化还原形式的pK值相同，这表明活性分子上两种底物具有相同的结合位点。类似物（果糖2,6 - 二磷酸）对两种底物都表现为竞争性抑制剂这一发现也支持了这一假设。当酶处于还原状态时，这种糖的抑制作用比氧化状态时更重要。当[Mg2 +]升高时观察到的最适pH值变化被解释为氧化型酶的构象变化，这通过荧光变化得以证明。还原型和氧化型相对于两种底物具有相同的理论反应速率，但还原型观察到的Vmax是理论Vmax的60%，而氧化型仅为理论Vmax的37%。还原型酶在催化方面似乎比氧化型酶更有效。
