Churchich J E, Scholz G, Kwok F
Department of Biochemistry, University of Tennessee, Knoxville 37996-08040.
Biochim Biophys Acta. 1989 Jul 6;996(3):181-6. doi: 10.1016/0167-4838(89)90245-8.
Brain pyridoxal kinase, which uses ATP complexed to either Zn(II) or Co(II) as substrates, displays high catalytic activity in the presence of Zn-thionein and Co-thionein. Several steps intervene in the process of pyridoxal kinase activation, i.e., binding of Zn ions to ATP and interaction between Zn-ATP and the enzyme. Equilibrium binding studies show that ATP mediates the release of Zn ions from the metal-thiolate clusters of the thioneins, whereas spectroscopic measurements conducted on Co-thionein reveal that the absorption transitions corresponding to the metal-thiolate of the protein are perturbed by ATP. The binding Zn-ATP to the kinase proceeds with a delta G = -6.3 kcal/mol as demonstrated by fluorometric titrations. Direct interaction between the kinase and derivatized-metallothionein could not be detected by emission anisotropy measurements, indicating that juxtaposition of the proteins does not influence the exchange of metal ions. Since the concentration of free Zn in several mammalian tissues is lower than 1 nM, it is postulated that under in vivo conditions the concentration of metallothionein regulates the catalytic activity of pyridoxal kinase.
脑吡哆醛激酶以与锌（II）或钴（II）络合的ATP作为底物，在锌硫蛋白和钴硫蛋白存在的情况下表现出高催化活性。吡哆醛激酶的激活过程涉及多个步骤，即锌离子与ATP的结合以及锌-ATP与酶之间的相互作用。平衡结合研究表明，ATP介导锌离子从硫蛋白的金属硫醇盐簇中释放出来，而对钴硫蛋白进行的光谱测量显示，与蛋白质金属硫醇盐相对应的吸收跃迁受到ATP的干扰。通过荧光滴定法证明，锌-ATP与激酶的结合过程中，ΔG = -6.3千卡/摩尔。通过发射各向异性测量无法检测到激酶与衍生化金属硫蛋白之间的直接相互作用，这表明蛋白质的并列排列不会影响金属离子的交换。由于几种哺乳动物组织中游离锌的浓度低于1 nM，因此推测在体内条件下，金属硫蛋白的浓度调节吡哆醛激酶的催化活性。
