Van Praag E, Tzur A, Zehavi U, Goren R
Kennedy-Leigh Centre for Horticultural Research, Rehovot, Israel.
IUBMB Life. 2000 Feb;49(2):149-52. doi: 10.1080/15216540050022485.
Shamouti phosphofructokinase (PFP) activation depends on the presence of fructose 2,6-bisphosphate (Fru-2,6-P2) in the glycolytic reaction. The effect of activation by Fru-2,6-P2 differs considerably, however, according to the buffer (pH 8.0) in which the reaction is performed: Ka = 2.77 +/- 0.3 nM in Hepes-NaOH and 7.75 +/- 1.49 nM in Tris-HCl. The presence of chloride ions (39 mM) in the Tris-HCl buffer inhibits PFP. Indeed, when using a Hepes-NaOH buffer and then adding 39 mM NaCl, Ka = 8.12 +/- 0.52 nM. The Ki for chloride ions is approximately 21.7 mM. In the gluconeogenic reaction, Shamouti PFP generally showed a high endogenous activity. Addition of Fru-2,6-P2 did not modify the velocity and the Vmax of the enzyme; however, its presence increased the affinity of the enzyme for Fru-1,6-P2 from 200 +/- 15.6 microM in absence of Fru-2,6-P2 to 89 +/- 10.3 microM in its presence (10 microM). In the presence of chloride (39 mM), the affinity for the substrate decreased with K(m) = 150 +/- 14 microM. The calculated Ki for chloride ions equals 56.9 mM. In both the glycolytic and the gluconeogenic reactions, Vmax is not affected; therefore, the inhibition mode of chloride is competitive.
沙姆蒂磷酸果糖激酶（PFP）的激活取决于糖酵解反应中果糖2,6 - 二磷酸（Fru - 2,6 - P2）的存在。然而，根据进行反应的缓冲液（pH 8.0）不同，Fru - 2,6 - P2的激活效果有很大差异：在Hepes - NaOH中Ka = 2.77±0.3 nM，在Tris - HCl中为7.75±1.49 nM。Tris - HCl缓冲液中氯离子（39 mM）的存在会抑制PFP。实际上，当使用Hepes - NaOH缓冲液然后添加39 mM NaCl时，Ka = 8.12±0.52 nM。氯离子的Ki约为21.7 mM。在糖异生反应中，沙姆蒂PFP通常表现出较高的内源性活性。添加Fru - 2,6 - P2不会改变酶的速度和Vmax；然而，它的存在会使酶对Fru - 1,6 - P2的亲和力从不存在Fru - 2,6 - P2时的200±15.6 μM增加到存在时（10 μM）的89±10.3 μM。在存在氯离子（39 mM）的情况下，对底物的亲和力降低，K(m)= 150±14 μM。计算得出的氯离子Ki等于56.9 mM。在糖酵解和糖异生反应中，Vmax均不受影响；因此，氯离子的抑制模式是竞争性的。
