Stability differences of muscle F-actin in formamide in the presence of Mg2+ and Ca2+ |
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| Affiliation: | 1. State Key Laboratory of Petroleum Resources and Engineering, Beijing, 102249, PR China;2. Key Lab of Petroleum Eng. of MOE, China University of Petroleum, Beijing, 102249, PR China;3. State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration and Development, Beijing, 100083, PR China;4. Development Research Department of CNOOC Research Institute Co., Ltd., Beijing, 100027, PR China;5. Bureau of Economic Geology, The University of Texas at Austin, 78705, United States;1. MOE Key Laboratory of Hydraulic Machinery Transients, School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei, 430072, China;2. School of Physic and Technology, Wuhan University, Wuhan, Hubei, 430072, China;3. School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore;4. Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China;1. Department of Organic Materials Science, Yamagata University, 4-3-16 Jonan, Yonezawa, Yamagata-ken 992-8510, Japan;2. Dipartimento di Chimica e Biologia, Università di Salerno, Via Giovanni Paolo II, 132, Fisciano 84084, Italy;3. Department of Fundamental Chemistry, Universidade Federal de Pernambuco, Cidade Universitária, Recife, PE 50740-560, Brazil;1. INQUINOA, Universidad Nacional de Tucumán, CONICET, DIPyGI-FACET-UNT, Av. Independencia 1800, C.P. 4000, San Miguel de Tucumán, Argentina;2. Laboratorio de Medios e Interfases (LAMEIN), DBI, FACET, Universidad Nacional de Tucumán, Instituto Superior de Investigaciones Biológicas (INSIBIO), CONICET, Av. Independencia 1800, C.P. 4000, San Miguel de Tucumán, Argentina |
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| Abstract: | Muscle G-actin was polymerized by addition of 2 mM Mg2+ or 2 mM Ca2+. Subsequent addition of formamide reduced the specific viscosity of the polymer solution. However, kinetic analysis of this reduction in the presence or absence of 0.1 M KCl revealed differences between F-actin formed in the presence of Mg2+ and F-actin formed in the presence of Ca2+. In the presence of Mg2+ the viscosity dropped instantaneously, reaching within minutes a steady-state level that was constant for many hours. In contrast, in the presence of Ca2+ the high-shear viscosity continued to decrease slowly after an initial drop, and it could take hours until a quasi-equilibrium was obtained. The time was dependent on both formamide and protein concentration. Addition of formamide increased the critical actin concentration in the presence of Ca2+, but not in the presence of Mg2+. This is taken as evidence that in the presence of Ca2+, but not in the presence of Mg2+, formamide causes partial depolymerization of F-actin. |
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