脑丙酮酸激酶的动力学特性
Kinetic properties of cerebral pyruvate kinase.
作者信息
Nicholas P C, Bachelard H S
出版信息
Biochem J. 1974 Jul;141(1):165-71. doi: 10.1042/bj1410165.
Partly purified guinea-pig brain pyruvate kinase is not activated by fructose 1,6-diphosphate and gives hyperbolic substrate-saturation curves with phosphoenolpyruvate. It is therefore different from the L-type pyruvate kinase of mammalian liver. Inhibition by MgATP(2-) was competitive for MgADP(-) but not for phosphoenolpyruvate, and the enzyme is therefore different from the M-type pyruvate kinase, which is said to be competitively inhibited by MgATP(2-) with respect to both substrates. The K(i)(MgATP(2-)) value of approx. 8mm for the brain enzyme is higher than the values (about 2mm) reported for the muscle enzyme. Stimulation of enzymic activity was observed at low (1-2mm) concentrations of MgATP(2-). Substrate kinetic constants were K(m) (MgADP(-))=0.47mm, K(m) (phosphoenolpyruvate)=0.08mm. Free Mg(2+) at very high concentrations (over 10mm) was inhibitory (K(i)=20-32mm). Neither ADP(3-) nor 5'-AMP(2-) inhibited the activity. The brain enzyme was concluded to be different from both the M-type and the L-type of other mammalian organs such as muscle and liver.
部分纯化的豚鼠脑丙酮酸激酶不会被1,6 - 二磷酸果糖激活，且与磷酸烯醇丙酮酸呈双曲线型底物饱和曲线。因此，它与哺乳动物肝脏的L型丙酮酸激酶不同。MgATP(2-)的抑制作用对MgADP(-)具有竞争性，但对磷酸烯醇丙酮酸无竞争性，所以该酶与M型丙酮酸激酶不同，据说M型丙酮酸激酶对两种底物均被MgATP(2-)竞争性抑制。脑酶的K(i)(MgATP(2-))值约为8mm，高于报道的肌肉酶的值（约2mm）。在低浓度（1 - 2mm）的MgATP(2-)下观察到酶活性的刺激作用。底物动力学常数为K(m)(MgADP(-)) = 0.47mm，K(m)(磷酸烯醇丙酮酸) = 0.08mm。极高浓度（超过10mm）的游离Mg(2+)具有抑制作用（K(i) = 20 - 32mm）。ADP(3-)和5'-AMP(2-)均不抑制该活性。结论是脑酶与其他哺乳动物器官（如肌肉和肝脏）的M型和L型均不同。
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