Product Release is Not the Rate-Limiting Step during
Cytochalasin B-Induced ATPase Activity of Monomeric Actin
Peter Dancker, Lore Hess
Institut für Z oologie der T echnischen H ochschule D arm stad t, S chn ittsp ah n straß e 10,
D -6100 D arm stad t, B undesrepublik D eutschland
and
Karl Ritter
M ax-P lanck-Institut für m edizinische F o rsch u n g , D-6900 H eidelberg,
B undesrepublik D eutschland
Z. N aturforsch. 46c, 139—144 (1991); received N ovem ber 12, 1990
A ctin, A T Pase A ctivity, N ucleo tid e Exchange
U n d er conditions w here cytochalasin B induces A T Pase activity o f m onom eric actin
(0.3 m M M gC l,, 1 m M E G T A , 30 (iM cytochalasin B, 1 m M A TP) the rate c o n stan t o f the ex­
change o f actin-boun d e-A T P for free A T P is a b o u t 4 - 6 times faster th an steady state A T P ase
activity. W hen a stoichiom etric A T P -actin com plex is extracted with PCA (single tu rn o v er ex­
perim ent) the ap p are n t rate c o n sta n t o f Pj generation is n o t faster than steady state A T Pase
activity. - The experim ents suggest th a t the hydrolysis o f actin-bound A TP an d not the subse­
quent release o f hydrolysis p ro d u c ts is rate-lim iting during cytochalasin-induced A T Pase activi­
ty o f actin.
Introduction
Cytochalasins are fungal metabolites which
strongly influence the behavior o f actin which is a
major protein of the motile and cytoskeletal appa­
ratus of eukaryotic cells. The most frequently used
cytochalasins are cytochalasin B and D. They have
the following three main effects: (1) At low con­
centrations they retard the growth of actin fila­
ments by slowing down m onom er addition to the
fast-growing end (the “barbed” end) of filaments
[1-5]. These findings suggest that cytochalasins
bind to filament ends and thus mimic the action of
“capping” proteins {cf. C ooper and Pollard [6],
Stossel et al. [7] for general reviews). (2) At concen­
trations which are more or less stoichiometric to
those of actin cytochalasin B and D accelerate
actin polymerization appreciably [8-12], This is
most probably due to accelerating the rate-limiting
nucleation step of actin polym erization [13, 14]. (3)
At the same stoichiometric concentrations cyto­
chalasins B and D induce an ATPase activity of
Abbreviations: E D T A , E thylenediam ine tetraacetic acid;
E G T A,
E thyleneglycol-bis-(2-am inoethylether)-N ,N 'tetraacetic acid; e-A T P, 1,N 6-eth en o ad en o sin e trip h o s­
phate; Pj, inorganic phosph ate; PC A , perchloric acid.
R eprint requests to D r. P. D ancker.
Verlag der Zeitschrift für N aturforschung, D-7400 Tübingen
0939-5075/91/0100-0139 $01.30/0
non-filamentous actin [8, 11]. Usually, actin cata­
lyzes ATP hydrolysis only in association with po­
lymerization. ATP which is originally bound to
each monomer is hydrolyzed shortly after incorpo­
ration into the growing filament. The hydrolysis
product ADP is normally not released at all and
the product phosphate is released in a delayed
manner (see Korn et al. [15], Carlier [16] for recent
reviews). Hence, during polymerization there is
only one turnover of ATP hydrolysis possible.
Cytochalasin B and D, however, induce a steady
ATPase activity uncoupled from polymerization.
The conditions under which this ATPase activity is
optimal (about 0.3 m M Mg:+, absence o f Ca2+,
about 30 |im of cytochalasin B) are similar to those
under which cytochalasin B accelerates actin poly­
merization. This suggests that induction of
ATPase activity and acceleration of polymeriza­
tion (by facilitating nucleus formation) are possi­
bly related. It is not yet clear whether dimers or
monomers are the true ATPase. G oddette and
Frieden [17] favor the first view whereas the strong
correlation of monomer concentration and
ATPase activity (Brenner and Korn [4], Dancker
and Kliche [18]) suggest that ATPase activity is a
property of monomers.
To date, relatively little is known about the
mechanism of ATPase activity o f cytochalasin-dependent ATPase activity. This com m unication ad-
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P. D an cker et al. - N ucleotide R elease a n d A T P ase A ctivity o f A ctin
dresses the question of the rate-limiting step by
com paring ATP hydrolysis and nucleotide ex­
change under conditions o f ATPase activity. We
present evidence that product release is not the
rate-limiting step of cytochalasin-induced ATPase
activity.
Methods and Materials
Actin from rabbit skeletal muscle was prepared
according to Pardee and Spudich [19]. Actin con­
centration was determined by optical absorption
at 290 nm using an extinction coefficient
=
0.63.
Preparation o f actin free of unbound ATP.
G-actin in G-buffer (2 m M Tris-HCl, pH 8.0,
0.1 m M ATP, 0.2 m M C aCl2, 1.5 m M N aN 3) was fil­
tered through a column (1 x 1 0 cm) containing the
anion exchanger Dowex 1 x 8 (200-400 mesh) to
remove unbound ATP and was collected in an
ATP-free G-puffer.
Preparation o f e-ATP-actin. G-actin from an
actin stock solution (about 5 mg/ml) in G-buffer
was diluted to 1 or 0.5 mg/ml with ATP-free
G-buffer. e-ATP (l,N 6-ethenoadenosine triphos­
phate) was added to 2 0 |j .m at least 1 h before
measuring nucleotide exchange.
M easurem ent of nucleotide exchange. Since the
discovery of Thames et al. [20] that the fluorescent
ATP analog e-ATP has a higher fluorescence
intensity when bound to actin than when free,
e-ATP is widely used in studies of nucleotide ex­
change of actin. We measured nucleotide exchange
by adding ATP to a cuvette containing e-ATP-ac­
tin and which was in a Shimadzu R F 520 double
beam fluorescence spectrophotom eter with excita­
tion and emission wavelength at 340 nm and
410 nm, respectively. Tem perature was 20 °C.
M easurement of ATP hydrolysis. Determ ina­
tion o f steady state ATPase activity has been de­
scribed in [18], “Single turnover experiments” are
performed as follows: The assays contained
0.5 mg/ml G-actin free o f unbound ATP in 0.3 m M
M gCl2, 5 m M Tris-HCl, pH 8, 1 m M EGTA. The
reaction (at 22 °C) was initiated by the addition of
actin to the other components. At different times
after the onset o f reaction 1 ml aliquots were add­
ed to 1 ml of ice-cold PCA (0.6 m ) . After centrifu­
gation the Pj content was determined with the mal­
achite green assay (K odam a et al. [21]): To 1 ml of
the supernatant o f the PCA extract 1 ml of m ala­
chite green reagent (see below) was added. After
40 min absorption was measured at 650 nm. The
phosphate standards contained the same com po­
nents as the enzymatic assay. For preparation of
the malachite green reagent 0.3 g o f malachite
green oxalate and 0.5 g Triton X-100 were dis­
solved in 1 1o f 0.7 m HC1.
D ata analysis. The time course o f fluorescence
decay or Pj generation during “single turnover” ex­
periments was fitted to a single exponential with a
non-linear regression program in order to obtain
the involved rate constants.
Materials. ATP, Dowex and cytochalasin B were
from Serva, Heidelberg, malachite green oxalate
and e-ATP were purchased from Sigma, Deisen­
hofen. All other chemicals were from Merck,
D arm stadt or Roth, Karlsruhe.
Results
During ATPase activity, release of the hydroly­
sis product ADP is an essential step. The kinetics
of nucleotide release can be inferred from experi­
ments on nucleotide exchange o f G-actin where actin-bound nucleotide is displaced by exogenous
nucleotide. M uch work has been devoted to this is­
sue (Kuehl and Gergely [22], Neidl and Engel [23],
W aechter and Engel [24], Frieden [25], Nowak et
al. [26], N ovak and G oody [27], Frieden and Patane [28]). M ost of this work has been done with
the fluorescent ATP analog e-ATP. The work of
these authors has shown that nucleotide exchange
obeys rather complex kinetics and is affected by di­
valent cations as well as by the concentration of
the displacing nucleotide (in most cases ATP). It is
still a m atter o f controversy whether nucleotides
are bound as metal ion complexes or whether nu­
cleotides and metal ions are bound at different
though interacting sites. The latter view is support­
ed by the work of Barden and dos Remedios [29],
the former view is supported by the work o f Loscalzo and Reed [30], Miki and Wahl [31], Brauer
and Sykes [32], Nowak and G oody [27],
The experiment of Fig. 1 shows that even in the
presence o f EDTA (which complexes both Ca and
Mg) there is rapid binding o f e-ATP (indicated by
a rapid rise in fluorescent intensity) to G-actin
which is too fast for the time resolution o f the re­
gistrations. This initial binding is followed by a
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P. D ancker et al. ■N u cleotide Release an d A T Pase A ctivity o f Actin
141
concentration of free Mg2+ is shown in Fig. 2. The
rate constant of the spontaneous loss of e-ATP
was the less the higher the concentration o f free
Mg2+. Cytochalasin B accelerated ATP release
45 S
Tim e
10
20
30
40
50
60
T im e ( s )
Fig. 1. Fluorescence o f G -actin after a d d itio n o f e-A TP
in the presence o f E D T A . - 20 ^xm o f e-A T P were added
to G -actin (0.5 m g/m l, 5 |i M T ris-H C l, pH 8.0, 10 |i m free
A TP) either sim ultaneously w ith 1 m M E D T A o r at v a r­
ious tim es after the ad d itio n o f E D T A . T he fluorescence
intensity which is reached after the a d d itio n o f e-A TP
(= peaks o f the single registrations, exam ples o f which
are show n in the inset) are plo tted against the time which
elapsed betw een E D T A ad d itio n an d e-A T P addition.
slower release of e-ATP. The curves resemble the
“ Bateman function” o f pharmacology which de­
scribes the sum of an initial “invasion” and a con­
secutive “evasion” of a pharm acon. Since the dis­
sociation o f CaATP or M gATP into its com po­
nents is fast, this experiment shows that ATP free
of metal ions is able to bind to actin albeit only
transiently. The longer the time period between
EDTA addition and ATP addition, the less ATP is
bound. This reflects the long-known fact {cf. [33])
that actin devoid of bound divalent cations under­
goes some kind of denaturation and loses its nu­
cleotides. This denaturation is also reflected by the
decreasing am ount of e-ATP which can initially be
bound. This am ount was the less the more time
elapsed between addition of EDTA and addition
of displacing ATP (Fig. 1). A lthough this decrease
cannot be fitted by an exponential as expected, the
general tendency is quite clear. This experiment
shows that as long as actin has still Mg and/or Ca
bound it is able to bind cation-free nucleotides.
There is no Ca- or Mg-complex o f nucleotides
necessary for nucleotide binding to occur.
The dependence of the stability of the actin-nucleotide complex on cytochalasin B and on the
Free Mg 2+ ( M )
Fig. 2. R ate co n stan ts o f the sp o n tan eo u s exponential
loss o f e-A TP b o u n d to G -actin as d ep en d en t on co n cen ­
tratio n o f free M g2+. — A fter treatm en t w ith a n io n ex­
changer actin was incubated w ith 20 ^m e-A T P fo r 1 h
and was passed once m ore th ro u g h the anion exchanger.
This e-A T P-actin free o f u n b o u n d nucleotide was added
to cuvettes co n tain in g 5 mM T ris-H C l, pH 8, 1 mM
E G T A , 1 m M E D T A and various co n cen tratio n s o f
MgCU to give the desired co n cen tratio n s o f free M g2+.
C ytochalasin B (CB) was either ab sen t o r 30 |aM. A n as­
sociation co n stan t o f 2.69 x 108 M_l for the M gE D T A
com plex was assum ed. Final actin co n cen tratio n was
0.5 m g/m l, tem p eratu re was 30 °C.
10-
MgCI2 (m M )
Fig. 3. Release o f e-A T P from actin after ad d itio n o f
1 m M A TP at different co n cen tratio n s o f M gC l2. - The
cuvettes contained 0.5 m g/m l e-A T P -G -actin, 5 m M
T ris-H C l, pH 8 and, if desired, 1 m M E G T A a n d /o r
30 (im cytochalasin B. • : no CB, no E G T A ; O: + CB, no
E G T A ; ■ : + E G T A , no CB; □ : + CB, + E G T A .
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142
only at higher Mg2+ concentrations where induc­
tion of ATPase activity can be expected to occur
dem onstrating that ADP-actin is less stable than
ATP-actin.
It is long known (cf.. [22, 23]) that C a2+ retards
the displacement of bound by free nucleotide.
Since cytochalasin B-induced ATPase activity is
inhibited by Ca2+ [8, 18] it is possible that these ef­
fects are interrelated. We therefore investigated the
displacement o f e-ATP by ATP under conditions
which are similar to those used in the ATPase ex­
periments.
Fig. 3 shows that 1 m M ATP displaces bound
e-ATP much faster in the presence of EGTA than
in its absence. The fact increasing Mg2+ concentra­
tions lowered the apparent rate constants of dis­
placement reflects the stabilizing effect of Mg2+ on
nucleotide binding.
Cytochalasin B had no effect on the displace­
ment rate. In the presence of 0.3 m M MgCl2, 1 m M
EGTA and 1 m M ATP (the standard conditions of
the ATPase experiments) the rate constant of the
exchange of bound for free ATP was 3.6 m in-1 in
this particular experiment, which was conducted
at 30 °C. M any experiments (not documented in
the paper) gave also at 20 °C rate constants in
T im e ( m in )
Fig. 4. G en eratio n o f inorganic p h o sp h ate (Pj) induced
by cytochalasin B. - The assays contained 0.5 mg/ml
(12 nm ol/m l) o f D ow ex-treated G -actin, 5 mM T ris-H C l,
pH 8, 0.3 mM MgCl-, 30 |iM C ytochalasin B an d either no
o r 1 mM E G T A . The rate co n stan ts for Pj generation
were 0 .1 6 m in " 1 (no E G T A ) an d 0 .4 4 m in " 1 (1 mM
E G T A present). The calculated end values are
10.6 nm ol m l" 1 (no E G T A ) and
11.0 n m o l-m l"1
(E G T A ), respectively; • : 1 mM E G T A present; O: no
E G T A present.
the range of 2 to 4 m in"1. Cytochalasin-induced
steady-state ATPase activity, however, is much
lower. It was under these conditions about 8 nmol
P, x mg actin-1 x m in"1 corresponding to a kc.dt of
about 0.3 m in-1 [18]. This is about 6 times slower
than an exchange rate of about 2 m in"1 (see
above). In other words: an ATP molecule has a
sixfold greater chance to become replaced by an­
other ATP than to become hydrolyzed. But still
the release of ADP could be rate-limiting if ADP
would be released much slower than ATP. Al­
though much evidence is against this possibility we
addressed the problem of the rate-limiting step by
performing a “single turnover” experiment. Free
ATP was removed from a G-actin solution by
treatment with an anion exchanger so that only actin-bound ATP remained and only one enzymatic
turnover was possible. We quenched the reaction
with acid and measured either the disappearance
of ATP by bioluminescence [34] or the appearance
of Pj (by the malachite green m ethod). Both ap­
proaches gave the same results. We show here only
experiments with Pj determ ination.
If ATP hydrolysis proper were much faster than
release of Pj, then in a single turnover experiment
P; should be liberated much faster than during
steady state (with many turnovers) since acid
would release also the phosphate which is still
bound at the enzyme. In other words, there should
be a fast phosphate burst the velocity of which
should exceed the steady state ATPase rate. If
ATP hydrolysis were rate-limiting, the rate of Pj
release and steady state ATPase activity should be
the same. From Fig. 4 it can be seen that in this
particular experiment P, release was 0.44 m in"1.
The Table summarizes the single turnover experiTable. G eneratio n o f Pj d u rin g “ single tu rn o v e r” experi­
m ents. C oncen tratio n s: D ow ex-treated actin 0.5 m g/m l
(= 12 |i m ); M gC l2: 0.3 m M ; E G T A : 1 m M ; T ris-H C l,
pH 8.0: 5 m M , cytochalasin: 30 (j m , no A T P was added, k
is the rate co n stan t o f the exponential tim e course o f P(
generation.
k [min ']
A m o u n t generated
[nm ol - m l"1]
0.44
0.46
0.40
0.30
0.29
11.6
14.5
8.34
6.9
6.9
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P. D ancker et al. ■N ucleotide R elease an d A T P ase A ctivity o f A ctin
ments and shows that the rate constants are be­
tween 0.3 and 0.4 m in“1. In other words, steady
state ATPase activity and generation of Pj are of
equal rates dem onstrating that ATP hydrolysis
and not product release is the rate-limiting step
during cytochalasin-induced ATPase activity of
monomeric actin.
Discussion
We have shown that under conditions where
cytochalasin B accelerates ATPase activity of
G-actin it does not accelerate nucleotide exchange
(see also Frieden [25]). This was the first hint that
during cytochalasin-induced ATPase activity
product release is not rate-limiting. This conclu­
sion is substantiated by the observation that ex­
change of s-ATP for exogenous ATP was much
faster than ATPase activity. Further, during single
turnover experiments, acid quenches revealed that
generation of phosphate is not faster than steady
state ATPase activity showing that ATP hydroly­
sis itself and not product release or a transition of
an ADP-P,-actin complex as Brenner and Korn
[35] supposed, is rate-limiting during cytochalasininduced ATPase activity. (That not in all experi­
ments the theoretical am ount of P; (12 nmol) was
produced indicates that Dowex treated actin loses
part o f its ATP already before the onset o f ATPase
activity.) This is rem arkable since other ATPase
activities have been shown to be rate-limited by
product release (e.g. myosin ATPase, Lymn and
Taylor [36], dynein ATPase, H olzbaur and John­
son [37]). ATPase activities o f actin which are sup­
posed to be rate-limited by product release are the
ATPase activity associated with m onom er addi­
tion to filament ends in the presence of cytochala­
sin D (Estes et al. [38]) and the ATPase activity of
monomeric actin induced by protam ine (Ferri
et al. [39]).
The fact that ATP hydrolysis and not product
release is the rate-limiting step of cytochalasin
B-induced ATPase activity implies that under
steady state conditions (excess o f ATP) ATP-actin
remains the prevailing species. Consider a simple
kinetic scheme of cytochalasin-induced ATPase
activity:
1
2
3
A + T -U A - T =-> A - D - P ,
A - D + P, ^
A + D + Pj
with A = actin, T = ATP, D = ADP. Step 2 is ratelimiting. When we neglect back reactions ATPase
activity during steady state equals the product of
the concentration of any intermediate and its for­
ward rate constant. Therefore ATPase activity v is
also
v = [A -D ] k4.
Since fluorescence does not discriminate between
e-ATP and s-ADP, the exchange rate E is
E = [A -T ] k _] + [A -D ]fc4.
If E is n times faster than v:
n [A -D ] k4 = [A -T ]
+ [A -D ] k4
or
[A -D ]/[A -T ] = k_ J (k 4( n - \) ) .
If the rate constants of A D P release and of ATP
release are more or less equal as Neidl and Engel
[23] assume then
[A -D ]/[A -T ] = l / ( « - l ) .
If ADP dissociates about 100 times faster than
ATP, as Nowak and Goody [27] assume (k4 ~
100 &_,) then
[A -D ]/[A -T ]=
1 /(1 0 0 (« -1 )).
Since n is about 4 to 6 there is in any case [A -T ] >
[A -D ], Since step 2 is rate-limiting, the concentra­
tion of ATP-actin (i.e. the interm ediate A -T ) is
higher than that of A D P-Pr actin (the intermediate
A - T - P j) , therefore, under the conditions of cytochalasin-induced ATPase activity the majority of
actin exists as ATP-actin, ADP-actin is only very
shortlived. Hence, effects of cytochalasin B on ac­
tin are not due to a conversion o f ATP-actin to
ADP-actin.
Acknowledgements
This work was supported by the Deutsche F o r­
schungsgemeinschaft.
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P. D an ck er et al. • N ucleotide Release and A T P ase A ctivity o f A ctin
[1] D. C. Lin, K. D. T ob in , D. G ru m et, and S. Lin,
J. Cell Biol. 84, 4 5 5 -4 6 0 (1 9 8 0 ).
[2] M. D. F lan ag an an d S. Lin, J. Biol. Chem . 255,
8 3 5 -8 3 8 (1 9 8 0 ).
[3] S. S. Brown an d J. A. Spudich, J. Cell Biol. 83, 6 5 7 662(1979).
[4] S. L. B renner a n d E. D. K o rn , J. Biol. Chem . 254,
9 9 8 2 -9 9 8 5 (1 9 7 9 ).
[5] S. M acL ean -F letch er an d T. D. P ollard, Cell 20,
3 2 9 -3 4 1 (1980).
[6] J. A. C o o p er an d T. D. P ollard, Biochem istry 24,
7 9 3 -7 9 9 (1 9 8 5 ).
[7] T. P. Stossel, C. C h ap o n n ier, R. M. Ezzell, J. H.
H artw ig, P. A. Janm ey, D. J. K w iatkow ski, S. E.
L ind, D. B. Sm ith, F. S. S outhw ick, H. L. Yin, and
K. S. Z aner, A nn. Rev. Cell Biol. 1, 3 5 3 -4 0 3 (1985).
[8] I. Low and P. D an ck er, Biochim. Biophys. A cta
4 3 0 ,3 6 6 -3 7 4 (1 9 7 6 ).
[9] R. T ellam and C. F rieden, Biochem istry 21, 3 2 0 7 3214(1982).
[10] J. F. T ait and C. F rieden, A rch. Biochem. Biophys.
2 1 6 ,1 3 3 -1 4 1 (1982).
[11] S. L. B renner an d E. D. K o rn , J. Biol. Chem . 255,
8 4 1 -8 4 4 (1 9 8 0 ).
[12] Y. Inoue, A. T ash iro , and K. M aru y am a, Biomed.
Res. 6, 3 4 3 -3 4 6 (1 9 8 5 ).
[13] P. D ancker an d I. Löw, Z. N atu rfo rsch . 34c, 555 —
557(1979).
[14] H. W endel an d P. D an ck er, Z. N aturfo rsch . 45c,
30 0 -3 0 2 (1 9 9 0 ).
[15] E. D. K orn, M . F. C arlier, an d D. P antaloni,
Science 238, 638 - 644 (1987).
[16] M. F. C arlier, Cell Biophysics 12, 1 0 5 - 117 (1988).
[17] D. F. G o d d ette an d C. F rieden, J. Biol. Chem . 261,
15 9 7 4 -1 5 9 8 0 (1 9 8 6 ).
[18] P. D ancker an d A. K üche, Z. N atu rfo rsch . 36c,
1050-1055(19 8 1 ).
[19] J. D. Pardee an d J. A. S pudich, M eth. Cell Biol. 24,
2 7 1 -2 8 9 (1 9 8 2 ).
[20] K. E. T ham es, H. C. C heung, and S. C. H arvey,
Biochem. Biophys. Res. C om m un. 60, 1252-1261
(1974).
21] T. K o d am a, K . F u k u i, an d K. K o m etan i, J. Bio­
chem. 99, 1 4 6 5 - 1472 (1986).
22] W. M. K ühl an d J. G ergely, J. Biol. C hem . 244,
4 7 2 0 -4 7 2 9 (1 9 6 9 ).
23] C. N eidl an d J. Engel, E ur. J. Biochem. 101, 1 6 3 169(1979).
24] F. W aechter a n d J. Engel, E ur. J. Biochem . 5 7 ,4 5 3 459(1975).
25] C. F rieden, J. Biol. C hem . 257, 2 8 8 2 -2 8 8 6 (1982).
26] E. N o w ak , H . S trzelecka-G olaszew ska, an d R. S.
G o o d y , B iochem istry 27, 1 7 8 5 - 1792 (1988).
27] E. N ow ak a n d R. S. G o o d y , Biochem istry 27,
7 6 1 3 -8 6 1 7 (1 9 8 8 ).
28] C. F rieden an d K. P atan e, B iochem istry 27, 3812—
3820(1988).
29] J. B arden an d C. G . dos R em edios, J. Biochem . 96,
9 1 3 -9 2 1 (1984).
30] J. Loscalzo an d G . H. R eed, Biochem istry 15,
5 4 0 7 -5 4 1 3 (1 9 7 6 ).
31] M. M iki a n d P. W ahl, Biochim . Biophys. A cta 828,
1 8 8 -1 9 5 (1985).
32] N. B rauer and B. D. Sykes, B iochem istry 21, 5 9 3 4 5939(1982).
33] H. S trzelecka-G olaszew ska, B. N agy, and J. G ergely,
A rch. Biochem . Biophys. 161, 5 5 9 -5 6 9 (1974).
34] H. W endel an d P. D ancker, Biochim. Biophys. A cta
915, 2 0 5 -2 0 9 (1 9 8 7 ).
35] S. L. B renner a n d E. D. K o rn , J. Biol. C hem . 256,
8 6 6 3 -8 6 7 0 (1 9 8 1 ).
36] R. W. Lym n a n d E. W. T ay lo r, B iochem istry 9,
2 9 7 5 -2 9 8 3 .
37] E. L. F. H o lz b au r an d K. A. Jo h n so n , Biochem istry
2 8 ,5 5 7 7 -5 5 8 5 (1 9 8 9 ).
38] J. E. Estes, L. A. Seiden, an d L. C. G ersh m an , in:
Actin: S tru ctu re a n d F u n ctio n in M uscle and N onM uscle Cells, pp. 1 6 9 -1 7 6 (1 9 8 3 ).
39] A. Ferri, E. M agri, an d E. G razi, Biochem. J. 183,
4 7 5 -4 7 6 (1 9 7 9 ).
Unauthenticated
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