Laham L E, Lamb J A, Allen P G, Janmey P A
Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts.
J Biol Chem. 1993 Jul 5;268(19):14202-7.
The rate of reaction and the stoichiometry of binding between gelsolin and actin monomers depends on adenine nucleotides. In the presence of Ca2+ but not Mg2+, gelsolin retains the ability to sever actin filaments when incubated for more than 20 min with an excess of G-actin in the presence of ATP but loses severing activity within seconds when mixed with G-actin in ADP. Immunoprecipitation of gelsolin removes more actin from ADP than from ATP solutions. Monomeric ATP-actin in 2 mM MgCl2 and 150 mM KCl slowly destroys the filament-severing activity of gelsolin with kinetics that are first order in actin concentration and with an apparent bimolecular rate constant of 0.021 +/- 0.007 microM-1 s-1. Coincident with the slow complex formation in MgCl2, the actin bound to the calcium-sensitive actin binding domain of gelsolin hydrolyzes its ATP to ADP. These results suggest a further level of gelsolin regulation and a functional similarity between actin and GTP-binding proteins.
凝溶胶蛋白与肌动蛋白单体之间的反应速率和结合化学计量取决于腺嘌呤核苷酸。在有Ca2+但无Mg2+存在的情况下，当在ATP存在下与过量的G-肌动蛋白孵育超过20分钟时，凝溶胶蛋白保留切断肌动蛋白丝的能力，但当与ADP中的G-肌动蛋白混合时，几秒钟内就会失去切断活性。凝溶胶蛋白的免疫沉淀从ADP溶液中去除的肌动蛋白比从ATP溶液中更多。在2 mM MgCl2和150 mM KCl中，单体ATP-肌动蛋白会缓慢破坏凝溶胶蛋白的丝切断活性，其动力学与肌动蛋白浓度呈一级关系，表观双分子速率常数为0.021±0.007 microM-1 s-1。与在MgCl2中缓慢形成复合物同时发生的是，与凝溶胶蛋白的钙敏感肌动蛋白结合结构域结合的肌动蛋白将其ATP水解为ADP。这些结果表明凝溶胶蛋白存在进一步的调节水平以及肌动蛋白与GTP结合蛋白之间的功能相似性。
