期刊
BIOPHYSICAL JOURNAL
卷 80, 期 2, 页码 841-851出版社
CELL PRESS
DOI: 10.1016/S0006-3495(01)76063-8
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Lowering pH or raising salt concentration stabilizes the F-actin structure by increasing the free energy change associated with its polymerization, To understand the F-actin stabilization mechanism, we studied the effect of pH, salt concentration, and cation species on the F-actin structure. X-ray fiber diffraction patterns recorded from highly ordered F-actin sols at high density enabled us to detect minute changes of diffraction intensities and to precisely determine the helical parameters. F-actin in a solution containing 30 mM NaCl at pH 8 was taken as the control. F-actin at pH 8, 30 to 90 mM NaCl or 30 mM KCl showed a helical symmetry of 2.161 subunits per turn of the 1-start helix (12.988 subunits/6 turns). Lowering pH from 8 to 6 or replacing NaCl by LiCl altered the helical symmetry to 2.159 subunits per turn (12.952/6). The diffraction intensity associated with the 27-Angstrom meridional layer-line increased as the pi-i decreased but decreased as the NaCl concentration increased. None of the solvent conditions tested gave rise to significant changes in the pitch of the left-handed 1-start helix (similar to 59.8 Angstrom). The present results indicate that the two factors that stabilize F-actin, relatively low pH and high salt concentration, have distinct effects on the F-actin structure. Possible mechanisms will be discussed to understand how F-actin is stabilized under these conditions.
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