Jy. Xu et al., MECHANICAL-PROPERTIES OF ACTIN FILAMENT NETWORKS DEPEND ON PREPARATION, POLYMERIZATION CONDITIONS, AND STORAGE OF ACTIN MONOMERS, Biophysical journal, 74(5), 1998, pp. 2731-2740
This study investigates possible sources for the variance of more than
two orders of magnitude in the published values for the shear moduli
of purified actin filaments. Two types of forced oscillatory rheometer
s used in some of our previous work agree within a factor of three for
identical samples. Polymers assembled in EGTA and Mg2+ from fresh, ge
l-filtered ATP-actin at 1 mg/ml typically have an elastic storage modu
lus (G') of similar to 1 Pa at a deformation frequency of 0.1-1 Hz. G'
is slightly higher when actin is polymerized in KCI with Ca2+ and Mg2
+. Gel filtration removes minor contaminants from actin but has little
effect on G' for most preparations of actin from acetone powder. Stor
age of actin monomers without frequent changes of buffer containing fr
esh ATP and dithiothreitol can result in changes that increase the G'
of filaments by more than a factor of 10. Frozen storage can preserve
the properties of monomeric actin, but care is necessary to prevent pr
otein denaturation or aggregation due to freezing or thawing.