pH值和游离镁离子对肌酸激酶反应以及其他磷酸水解和磷酸转移反应的平衡常数的影响。

Effects of pH and free Mg2+ on the Keq of the creatine kinase reaction and other phosphate hydrolyses and phosphate transfer reactions.

作者信息

Lawson J W, Veech R L

出版信息

J Biol Chem. 1979 Jul 25;254(14):6528-37.

Abstract

The observed equilibrium constants (Kobs) of the creatine kinase (EC 2.7.3.2), myokinase (EC 2.7.4.3), glucose-6-phosphatase (EC 3.1.3.9), and fructose-1,6-diphosphatase (EC 3.1.3.11) reactions have been determined at 38 degrees C, pH 7.0, ionic strength 0.25, and varying free magnesium concentrations. The equilibrium constant (KCK) for the creatine kinase reaction defined as: KCK = [sigma ATP] [sigma creatine] divided by ([sigma ADP] [sigma creatine-P] [H+]) was measured at 0.25 ionic strength and 38 degrees C and was shown to vary with free [Mg2+]. The value was found to be 3.78 x 10(8) M-1 at free [Mg2+] = 0 and 1.66 x 10(9) M-1 at free [Mg2+] = 10(-3) M. Therefore, at pH 7.0, the value of Kobs, defined as Kobs = KCK[H+] = [sigma ATP] [sigma creatine] divided by ([sigma ADP] [sigma creatine-P] was 37.8 at free [Mg2+] = 0 and 166 at free [Mg2+] = 10(-3) M. The Kobs value for the myokinase reaction, 2 sigma ADP equilibrium sigma AMP + sigma ATP, was found to vary with free [Mg2+], being 0.391 at free [Mg2+] = 0 and 1.05 at free [Mg2+] = 10(-3) M. Taking the standard state of water to have activity equal to 1, the Kobs of glucose-6-P hydrolysis, sigma glucose-6-P + H2O equilibrium sigma glucose + sigma Pi, was found not to vary with free [Mg2+], being 110 M at both free [Mg2+] = 0 and free [Mg2+] = 10(-3) M. The Kobs of fructose-1,6-P2 hydrolysis, sigma fructose-1,6-P2 equilibrium sigma fructose-6-P + sigma Pi, was found to vary with free [Mg2+], being 272 M at free [Mg2+] = 0 and 174 M at free [Mg2+] = 0.89 x 10(-3) M.

摘要

已在38摄氏度、pH值7.0、离子强度0.25以及不同游离镁浓度条件下，测定了肌酸激酶（EC 2.7.3.2）、肌激酶（EC 2.7.4.3）、葡萄糖-6-磷酸酶（EC 3.1.3.9）和果糖-1,6-二磷酸酶（EC 3.1.3.11）反应的观测平衡常数（Kobs）。肌酸激酶反应的平衡常数（KCK）定义为：KCK = [总ATP] [总肌酸] 除以（[总ADP] [总磷酸肌酸] [H⁺]），在离子强度0.25和38摄氏度下进行了测定，结果表明其随游离[Mg²⁺]而变化。当游离[Mg²⁺] = 0时，该值为3.78×10⁸ M⁻¹；当游离[Mg²⁺] = 10⁻³ M时，该值为1.66×10⁹ M⁻¹。因此，在pH值7.0时，定义为Kobs = KCK[H⁺] = [总ATP] [总肌酸] 除以（[总ADP] [总磷酸肌酸]）的Kobs值，在游离[Mg²⁺] = 0时为37.8，在游离[Mg²⁺] = 10⁻³ M时为166。肌激酶反应2总ADP ⇌ 总AMP + 总ATP的Kobs值随游离[Mg²⁺]而变化，在游离[Mg²⁺] = 0时为0.391，在游离[Mg²⁺] = 10⁻³ M时为1.05。将水的标准态活度设为1，葡萄糖-6-磷酸水解反应（总葡萄糖-6-磷酸 + H₂O ⇌ 总葡萄糖 + 总磷酸）的Kobs值不随游离[Mg²⁺]变化，在游离[Mg²⁺] = 0和游离[Mg²⁺] = 10⁻³ M时均为110 M。果糖-1,6-二磷酸水解反应（总果糖-1,6-二磷酸 ⇌ 总果糖-6-磷酸 + 总磷酸）的Kobs值随游离[Mg²⁺]变化，在游离[Mg²⁺] = 0时为272 M，在游离[Mg²⁺] = 0.89×10⁻³ M时为174 M。