Chernikevich I P, Makarchikov A F
Institute of Biochemistry, Academy of Sciences of Belarus, Grodno.
Ukr Biokhim Zh (1978). 1997 Sep-Dec;69(5-6):41-50.
The steady-state kinetics of the ThTP hydrolysis by thiamine triphosphatase (EC 3.6.1.28) from bovine brain testified to the presence of two kinetically significant conformational states of the protein, their equilibrium being determined by the substrate concentration. The ThTPase isomeric forms had different activities, affinities for ThTP and activation energies. The form with high affinity for the substrate was characterized by the Km and Vmax values of 43 microM and 9.9 mumol.s-1.mg-1 whereas for the form with lower affinity these values were equal to 298 microM and 19.3 mumol.s-1.mg-1, respectively. The activation energies of the ThTP hydrolysis reactions were 85.3 and 47.1 kJ.mol-1. Several mechanisms of the enzyme activity regulation in the cell are suggested. One of the mechanisms is related to the allosteric ThTP effect inducing reversible transition of the protein to a more active conformational state, while the others include the inhibition activity by ATP and the activation of ThTP-ase by Mg2+ free ions.
来自牛脑的硫胺素三磷酸酶（EC 3.6.1.28）对硫胺素三磷酸（ThTP）水解的稳态动力学证明，该蛋白质存在两种具有动力学意义的构象状态，它们的平衡由底物浓度决定。硫胺素三磷酸酶的异构形式具有不同的活性、对硫胺素三磷酸的亲和力和活化能。对底物具有高亲和力的形式的Km和Vmax值分别为43微摩尔和9.9微摩尔·秒⁻¹·毫克⁻¹，而对亲和力较低的形式，这些值分别等于298微摩尔和19.3微摩尔·秒⁻¹·毫克⁻¹。硫胺素三磷酸水解反应的活化能分别为85.3和47.1千焦·摩尔⁻¹。文中提出了细胞中酶活性调节的几种机制。其中一种机制与变构硫胺素三磷酸效应有关，该效应诱导蛋白质可逆转变为更具活性的构象状态，而其他机制包括ATP的抑制活性和游离镁离子对硫胺素三磷酸酶的激活。
