1: J Mol Biol  1984 Nov 5;179(3):453-67 

Torsional motion of eosin-labeled F-actin as detected in the time-resolved
anisotropy decay of the probe in the sub-millisecond time range.

Yoshimura H, Nishio T, Mihashi K, Kinosita K Jr, Ikegami A.

The internal motion of F-actin in the time range from 10(-6) to 10(-3) second
has been explored by measuring the transient absorption anisotropy of
eosin-labeled F-actin using laser flash photolysis. The transient absorption
anisotropy of eosin-F-actin at 20 degrees C has a component that decays in the
submicrosecond time scale to an anisotropy of about 0.3. This anisotropy then
decays with a relaxation time of about 450 microseconds to a residual anisotropy
of about 0.1 after 2 ms. When the concentration of eosin-F-actin was varied in
the range from 7 to 28 microM, the transient absorption anisotropy curves
obtained were almost indistinguishable from each other. These results show that
the anisotropy decay arises from internal motion of eosin-F-actin. Analysis of
the transient absorption anisotropy curves indicates that the internal motion
detected by the decay in anisotropy is primarily a twisting of actin protomers
in the F-actin helix; bending of the actin filament makes a minor contribution
only to the measured decay. The torsional rigidity calculated from the transient
absorption anisotropy is 0.2 X 10(-17) dyn cm2 at 20 degrees C, which is about
an order of magnitude smaller than the flexural rigidity determined from
previous studies. Thus, we conclude that F-actin is more flexible in twisting
than in bending. The calculated root-mean-square fluctuation of the torsional
angle between adjacent actin protomers in the actin helix is about 4 degrees at
20 degrees C. We also found that the torsional rigidity is approximately
constant in the temperature range from 5 to approximately 35 degrees C, and that
the binding of phalloidin does not appreciably affect the torsional motion of
F-actin.

PMID: 6210369 [PubMed - indexed for MEDLINE]