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首页> 外文期刊>Biochemistry >ACID-BASE CATALYTIC MECHANISM AND PH DEPENDENCE OF FRUCTOSE 2,6-BISPHOSPHATE ACTIVATION OF THE ASCARIS SUUM PHOSPHOFRUCTOKINASE
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ACID-BASE CATALYTIC MECHANISM AND PH DEPENDENCE OF FRUCTOSE 2,6-BISPHOSPHATE ACTIVATION OF THE ASCARIS SUUM PHOSPHOFRUCTOKINASE

机译：天蓝色蔗糖磷酸激酶对果糖2,6-双磷酸酯活化的酸基催化机理和pH依赖性

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A form of phosphofructokinase (PFK) from Ascaris suum desensitized to hysteresis in the reaction time course and ATP allosteric inhibition has been used to study the activation by fructose 2,6-bisphosphate (F26P(2)) at varied pH in both reaction directions. In the direction of phosphorylation of F6P, V and V/K-MgATP are constant over the pH range 6-9, while V/K-F6P decreases at low pH, giving a pK value of 7.0, and at high pH, giving a pK of 8.9. V and V/K-MgATP are insensitive to the presence of F26P(2), but V/K-F6P is increased by a constant amount in the presence of saturating F26P(2) over the entire pH range studied. The concentration of F26P(2) that gives half the change in V/K-F6P, K-act, increases as the pH decreases, giving a pK of 7.4, reflecting an enzyme group that must be unprotonated for optimum binding of F26P(2). In the direction of phosphorylation of MgADP, V and V/K-MgADP are pH-independent, and both are insensitive to the presence of F26P(2). V/K-FBP decreases at high pH, giving a pK of about 7.3, and is increased by a constant amount in the presence of F26P(2) over the entire pH range studied. A mechanism consistent with the data requires an enzymic general base with a pK of 7.0 to accept a proton from the 1-hydroxyl of F6P concomitant with nucleophilic attack of the hydroxyl on the gamma-phosphate of MgATP, while a second enzyme group with a pK of 8.9 must be protonated and is postulated either to neutralize the negative charge on the gamma-phosphate of MgATP to facilitate the nucleophilic attack or to bind the 6-phosphate of F6P. A group with a pK of 7.4 in the F26P(2) binding site must be unprotonated for optimum binding of the effector and likely hydrogen-bonds to the hydroxyl group at C1, C2, or C3 of F26P(2). The effect of F26P(2) is the pH-independent decrease of the off rate for F6P and FBP from binary and ternary enzyme-reactant complexes.
机译：来自A虫的磷酸果糖激酶（PFK）的一种形式在反应时间过程中对磁滞脱敏，并且ATP变构抑制作用已被用于研究果糖2,6-双磷酸酯（F26P（2））在两个反应方向的不同pH下的活化。在F6P磷酸化的方向上，V和V / K-MgATP在6-9的pH范围内保持恒定，而V / K-F6P在低pH值下降低，pK值为7.0，在高pH值下给出pK值。 PK为8.9。 V和V / K-MgATP对F26P（2）的存在不敏感，但在整个研究的pH范围内，在存在饱和F26P（2）的情况下，V / K-F6P会以恒定的量增加。 F / K-F6P（K-act）变化一半的F26P（2）浓度随pH降低而增加，pK为7.4，反映了为实现F26P（2）的最佳结合而必须未质子化的酶基团）。在MgADP的磷酸化方向上，V和V / K-MgADP不依赖于pH，并且对F26P（2）的存在均不敏感。在高pH下，V / K-FBP降低，pK约为7.3，在整个研究的pH范围内，在F26P（2）存在下，V / K-FBP均以恒定量增加。与数据一致的机制要求酶促通用碱基的pK为7.0，以接受来自F6P 1-羟基的质子，伴随羟基对MgATP的γ-磷酸的亲核攻击，而第二个酶基具有pK 8.9的分子必须被质子化，并被假定为中和MgATP的γ-磷酸上的负电荷以促进亲核攻击或结合F6P的6-磷酸。 F26P（2）结合位点的pK为7.4的基团必须未质子化，以实现效应物的最佳结合，并且可能与F26P（2）的C1，C2或C3处的氢键形成氢键。 F26P（2）的作用是F6P和FBP从二元和三元酶反应物复合物中解离速率的pH依赖性降低。

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