Changes in conformation and nucleotide binding of Ca, Mn, or MgG-actin upon removal of the bound divalent cation. Studies of ultraviolet difference spectra and optical rotation |
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Authors: | H Strzelecka-Golaszewska B Nagy J Gergely |
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Institution: | 1. Department of Muscle Research, Boston Biomedical Research Institute Boston, Massachusetts 02114 USA;2. Department of Neurology, Massachusetts General Hospital Boston, Massachusetts 02114 USA;3. Departments of Neurology and Biological Chemistry, Harvard Medical School, Boston, Massachusetts 02114 USA |
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Abstract: | The ultraviolet difference spectra of EDTA-induced denaturation of dithiothreitoltreated actin prepared with either Ca2+, Mn2+, or Mg2+ as the strongly bound cation showed no appreciable difference, nor could any difference be found in the change of optical rotation. However, at different wavelengths the changes in the spectra have different rates and these rates do differ significantly depending on the bivalent cation bound to G-actin. The nucleotide and the cation appear to be removed simultaneously and at the fastest rate; about 50–80% is released within 1 min. The spectral changes have two phases: a fast change whose detailed kinetics have not been investigated in this paper, followed by a slower rate with first-order kinetics. The changes of optical rotation follow a single-phase first-order kinetics. The rates depend on the divalent cation, the sequence being Mn2+ > Ca2+ > Mg2+. ATP release is partially reversible upon Ca2+ addition; the reversibility is diminished as the time of incubation with EDTA is increased. On rebinding of ATP and Ca2+, the spectral and optical rotatory changes are not reversed, but no further changes occur. Such an EDTA-treated actin is polymerizable after addition of Ca2+, and the G-actin obtained after polymerization and depolymerization shows the same spectral change on a second addition of EDTA as the original actin. On the basis of these observations a scheme is suggested for the denaturation of G-actin. |
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Keywords: | Please address reprint requests to the Boston Biomedical Research Institute 20 Staniford Street Boston MA 02114 |
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