Chemistry Reference
In-Depth Information
repetitive change in three FRET levels (H, M, and L), indicating the 120
step rotation
during ATP synthesis; this result is consistent with the very low friction of the F
o
component reported in another study [49]. The order of the three FRET levels (L-H-M-
L) was reversedwhen the rotationwas driven by ATP hydrolysis (L-M-H-L), indicating
that the rotational direction is reversed in ATP synthesis.
Although the above experiment proved that the rotation of F
o
F
1
is driven by the
proton motive force, many issues remain to be resolved. For example, the depen-
dence of the rotational speed on the proton motive force and the composition of
nucleotides and Pi, and the conditions under which the rotational direction is
reversed have not yet been examined. Furthermore, the 80
and 40
substeps found
in the rotation driven by ATP hydrolysis remain to be observed, and the reversibility of
the reaction scheme betweenATP hydrolysis and synthesis has not been investigated.
10.3
Perspectives
As a biological molecular machine, ATP synthase has always been a topic of interest
in basic and applied research. Although extensive analysis using single-molecule
measurements has revealed various properties of F
1
, many issues remain to be
resolved; these include the determination of how the three
subunits cooperate in
the ATP-driven rotation of F
1
, and particularly how the protonmotive force drives the
rotation of F
o
and F
o
F
1
. Direct observation can provide valuable insights and needs to
be achieved as soon as possible. Structural information relating to F
o
and the F
o
F
1
complex at the atomic scale and computational study of conformational and rota-
tional dynamics are also indispensable. Many more studies will be needed in order to
understand this splendid molecular machine.
b
Acknowledgments
We thank Drs Hiromasa Yagi, Nobuto Kajiwara, and Hideo Akutsu, (Osaka Univer-
sity) for providing their unpublished results. We also thank Drs Masasuke Yoshida
(Tokyo Institute of Technology), Katsuya Shimabukuro (Florida State University),
Yasuyuki Kato-Yamada (Rikkyo University), and Drs Daichi Okuno, Kazuhito Tabata,
Hiromi Imamura, and Hiroshi Ueno in our laboratory for helpful discussions.
References
1 Boyer, P.D. (1997) The ATP synthase
a
splendid molecular machine. Annu. Rev.
Biochem.,
-
rotary engine of the cell. Nat. Rev. Mol. Cell
Biol.,
677.
3 Capaldi, R.A. and Aggeler, R. (2002)
Mechanism of the F(1)F(0)-type
ATP synthase, a biological rotary
2
, 669
-
749.
2 Yoshida, M., Muneyuki, E., and Hisabori,
T. (2001) ATP synthase
66
, 717
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a marvelous
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