Chemistry Reference
In-Depth Information
Figure 10.1 Schematic structure of ATP synthase.
ATP synthase (left) is composed of two rotary
motors. F
o
(upper right) is embedded in the cell
membrane and rotates with the translocation of
proton, and is driven by proton motive force. The
protonmotive force is formed by the difference in
proton concentration (DpH) and membrane
potential (DY)acrossthemembrane.F
1
(lower
right) rotates with ATP hydrolysis. Note that the
rotational direction of F
o
is opposite to that of F
1
.
The rotor and stator subunits are shown in red and
green, respectively.
the electrochemical potential gradient of the protons (or Na ions in several
species). This potential gradient, which is often termed the proton motive force,
is generated by respiratory chain or photosynthesis [4]. The rotational direction of
F
o
is opposite to that of F
1
driven by ATP hydrolysis. Generally, the proton motive
force is large in vivo, and F
o
generates a larger torque than F
1
and forcibly rotates F
1
in
the reverse direction, thereby catalyzing the reverse chemical reaction, i.e. ATP
synthesis.
10.1.2
Boyers Proposal and Walkers Crystal Structure
Approximately three decades ago, the rotational catalysis of F
1
(and ATP synthase)
was
rst proposed by Paul Boyer, as a result of his studies on binding change
mechanism for ATP synthase [5]. His model had two central features. First, the
energy required for ATP synthesis is mainly used to promote the binding of
substrates (ADP and Pi) and the release of the tightly bound product (ATP). Second,
the three catalytic
subunits of ATP synthase participate in the reaction in a highly
cooperative manner. According to these features, each of the catalytic sites alternately
changes the af
nity to nucleotides and Pi, coupled with energy input/output. To
substantiate this model Boyer proposed that the asymmetric central
b
gde
subunit of
ATP synthase rotates against the surrounding catalytic
b
subunits to cause sequential
change. To date, in addition to the
g
subunit, rotation of the
e
subunit has also been
observed.
