Research and Development, Gilead Sciences, Inc., 333 Lakeside Drive, Foster City, CA 94404, USA.
Arch Biochem Biophys. 2011 Feb 15;506(2):130-6. doi: 10.1016/j.abb.2010.11.008. Epub 2010 Nov 21.
Many of the cellular responses to Ca++ signaling are modulated by a family of multifunctional Ca++/calmodulin dependent protein kinases (CaMKs): CaMK I, CaMK II and CaMK IV. In order to further understand the role of CaMKs, we investigated the kinetic mechanism of CaMK II isozymes in comparison with those of CaMK I and CaMK IV by analyzing their steady state kinetics using phospholamban as a phosphoacceptor. The results indicated that (a) the CaMK family's reaction mechanisms were of the sequential type in which all substrates must bind to enzyme before any product is released; (b) CaMK I and CaMK IV exhibited random sequential mechanism where either phospholamban or ATP can bind to the free enzyme; (c) the data of product inhibition for CaMK IIs best fit with an Ordered Bi Bi mechanism in which phospholamban is the first substrate to bind and ADP is the last product to be released; and (d) the constant α (ratio of apparent dissociation constants for binding peptide in the presence and absence of the second ligand) of all isozymes for ATP and peptide was higher than 1 indicating that the binding of phospholamban to CaMK decreased the enzyme's affinity toward ATP.
许多细胞对钙信号的反应是由一组多功能钙/钙调蛋白依赖蛋白激酶（CaMKs）调节的：CaMK I、CaMK II 和 CaMK IV。为了进一步了解 CaMKs 的作用，我们通过分析磷酸化酶抑制剂作为磷酸受体的稳态动力学，比较了 CaMK II 同工酶与 CaMK I 和 CaMK IV 的动力学机制。结果表明：(a) CaMK 家族的反应机制为顺序型，所有底物必须在释放任何产物之前结合酶；(b) CaMK I 和 CaMK IV 表现出随机顺序机制，磷酸化酶抑制剂或 ATP 均可结合游离酶；(c) CaMK II 的产物抑制数据最符合有序双位点双位点机制，其中磷酸化酶抑制剂是第一个结合的底物，ADP 是最后释放的产物；(d) 所有同工酶的常数α（在存在和不存在第二个配体的情况下，肽结合的表观解离常数的比值）对于 ATP 和肽均高于 1，表明磷酸化酶抑制剂与 CaMK 的结合降低了酶对 ATP 的亲和力。
