Chardot T, Meunier J C
Institut National Agronomique Paris-Grignon, Centre de Biotechnologie Agro-Industrielle (C.B.A.I.), Thiverval-Grignon, France.
Biochem J. 1991 Sep 15;278 ( Pt 3)(Pt 3):787-91. doi: 10.1042/bj2780787.
Fructose-1,6-bisphosphatase (FBPase) can be reduced and activated by either dithiothreitol or reduced thioredoxin. This activation is pH-dependent. An amino acid group with a pK value of 5.55 is involved in this process. Both enzyme forms can also be stimulated by agents such as fructose 1,6-bisphosphate, Mg2+, Ca2+ and Ca2+/fructose 1,6-bisphosphate. FBPase reduced by dithiothreitol is more strongly activated than the enzyme reduced by thioredoxin. The specificity constant (kcat./Km) is enhanced over 2.5-25-fold and 1.5-2-fold (depending on the agent used) for FBPase reduced by dithiothreitol and thioredoxin respectively. In both cases, no new kinetic properties appeared. The pH-activity profile of the stimulated enzyme is slightly shifted towards the acidic side with respect to the reduced enzyme. A lag phase is observed in the progress curve of both enzymic forms, treated or untreated. Each agent used to stimulate must induce a new conformation of the enzyme, more active than the initial one, characterized by a specificity constant and a relaxation time. This lag phase tends to disappear when the assay temperature is increased. Temperature has the same effect on the activity of oxidized, reduced and stimulated FBPase, but different effects on the stability of the different forms.
果糖-1,6-二磷酸酶（FBPase）可被二硫苏糖醇或还原型硫氧还蛋白还原并激活。这种激活作用依赖于pH值。一个pK值为5.55的氨基酸基团参与了这一过程。两种酶形式也可被果糖1,6-二磷酸、Mg2+、Ca2+和Ca2+/果糖1,6-二磷酸等试剂刺激。经二硫苏糖醇还原的FBPase比经硫氧还蛋白还原的酶激活作用更强。对于分别经二硫苏糖醇和硫氧还蛋白还原的FBPase，其特异性常数（kcat./Km）分别提高了2.5至25倍和1.5至2倍（取决于所用试剂）。在这两种情况下，均未出现新的动力学特性。与还原型酶相比，受刺激酶的pH-活性曲线略微向酸性一侧偏移。在经处理或未处理的两种酶形式的进程曲线中均观察到一个滞后期。用于刺激的每种试剂都必须诱导酶形成一种新的构象，这种构象比初始构象更具活性，其特征在于特异性常数和弛豫时间。当测定温度升高时，这个滞后期往往会消失。温度对氧化型、还原型和受刺激型FBPase的活性有相同的影响，但对不同形式的稳定性有不同的影响。
