Hathaway G M, Traugh J A
Arch Biochem Biophys. 1984 Aug 15;233(1):133-8. doi: 10.1016/0003-9861(84)90609-x.
In reticulocytes, polyamines appear to be physiologically relevant activators of casein kinase II [Hathaway, G. M. and Traugh, J. A. (1984). J. Biol. Chem. 259, 7011-7015]. The mechanism by which polyamines and Mg2+ interact to activate casein kinase II has been investigated. These studies were conducted by holding ionic strength constant at 0.10 M. At low Mg2+ (2.5 mM), activation by spermine resulted in a 33% decrease in the apparent Km for casein. Under these conditions, a 2.3-fold increase in the maximum velocity of the reaction was observed, and half-maximal stimulation was obtained with 275 microM spermine. At a kinetically optimal Mg2+ concentration of 12.5 mM, the effects of spermine on Km and Vmax were reduced, and the concentration of spermine required to give 50% of maximal stimulation was increased to 750 microM. Kinetic data obtained at the two Mg2+ concentrations indicated that Mg2+ and spermine competed for the same form of the enzyme. Double-reciprocal plots of velocity versus Mg2+ concentration showed downward curvature at Mg2+ concentrations higher than 1 mM, and these results were interpreted as evidence for two binding sites on the enzyme with an apparent Km of 0.5 and 2.5 mM. Experiments carried out with ATP-Mg2+ in the absence of excess MgCl2 gave results consistent with an absolute requirement of the enzyme for the metal ion which could not be replaced by spermine. These results are consistent with the formation of an enzyme-activator complex. A model is proposed where spermine activates casein kinase II at one site on the enzyme at which MgCl2 can also bind, while a second, high-affinity site exists exclusively for the metal ion.
在网织红细胞中，多胺似乎是酪蛋白激酶II的生理相关激活剂[哈瑟韦，G.M.和特劳，J.A.（1984年）。《生物化学杂志》259卷，7011 - 7015页]。已经研究了多胺和Mg2 +相互作用激活酪蛋白激酶II的机制。这些研究是在离子强度保持恒定为0.10 M的条件下进行的。在低Mg2 +（2.5 mM）时，精胺激活导致酪蛋白的表观Km降低33%。在这些条件下，观察到反应的最大速度增加了2.3倍，用275 microM精胺可获得半最大刺激。在动力学最佳Mg2 +浓度12.5 mM时，精胺对Km和Vmax的影响降低，产生50%最大刺激所需的精胺浓度增加到750 microM。在两种Mg2 +浓度下获得的动力学数据表明，Mg2 +和精胺竞争酶的同一形式。速度与Mg2 +浓度的双倒数图在Mg2 +浓度高于1 mM时显示向下弯曲，这些结果被解释为酶上存在两个结合位点的证据，其表观Km分别为0.5和2.5 mM。在没有过量MgCl2的情况下用ATP - Mg2 +进行的实验结果表明，该酶绝对需要金属离子，而精胺不能替代。这些结果与酶 - 激活剂复合物的形成一致。提出了一个模型，其中精胺在酶上的一个位点激活酪蛋白激酶II，MgCl2也可结合于此，而另一个高亲和力位点仅用于金属离子。
