|Mabuchi, I. (1983) An actin-depolymerixing protein
(depactin) from starfish oocytes: Properties and interaction with actin.
J.Cell Biol. 97, 1612-1621
|Physico-chemical properties and interaction with actin of
an actin-depolymerizing protein from mature starfish oocyte were
studied. This protein, which is called depactin, exists in a monomeric
form under physiological conditions. Its molecular weight is
~20,000 for the native protein and ~17,000 for denatured protein.
The Glu + Asp/Lys + Arg molar ratio of this protein is 1.55. The
apparent pI of the denatured depactin is ~6.
The extent of actin polymerization is reduced by the presence of
depactin; however, the rate of polymerization seems to be accelerated as
measured spectrophotometrically at 238nm. This effect is interpreted to
indicate that depactin cut the newly formed filaments into small
fragments, thereby increasing the number of the filament ends onto which
monomers are added. The apparent critical concentration of actin
for polymerization, as determined by viscometry or flow birefringence
measurement, is increased by the presence of depactin in a
concentration-dependent manner. Raising the pH of the solution
does not reverse the action of depactin. The molar ratio of actin
and depactin, which interact with each other, is estimated to be 1:1 by
means of a cross-linking experiment using a water-soluble carbodiimide.
Depactin binds to a DNase I-sepharose column via actin and is
selectively eluted with 0.6M KCl or 0.6M KI. The association constant
between actin and depactin is estimated, using the column, to be
The constant of depactin in the high-speed supernatant of the oocyte
extract is determined to be 1%; this can act upon ~63% of the actin in