Chemistry Reference
In-Depth Information
Figure 10.8 ATP synthesis by a single F
1
molecule
forced to rotate in the reverse direction.
(A) Schematic representation of the experimental
set-up. F
1
enclosed in the femtoliter chamber
was forced to rotate in the ATP synthesis direction
by using magnetic tweezers in the presence of
ADP, Pi, and a small amount of ATP. The newly
synthesized ATP was accumulated in the
chamber. (B) After the forced rotation, the
rotational speed by ATP hydrolysis increased
(1 to 4). When F
1
was released from the chamber,
the rotational speed decreased and returned to
the level before the enclosure. The number of
synthesized ATP molecules was estimated from
the increment in rotational speed. (C and D) The
number of ATP molecules synthesized by the
a
3
b
3
g
(D) subcomplexes of F
1
after the forced reverse rotation. Each trace
represents the data from individual F
1
.Dotted
lines indicate the slopes where the coupling ratio
was expected to be 0% (0 ATP/turn), 50% (1.5
ATP/turn), and 100% (3 ATP/turn).
(C) and
a
3
b
3
ge
The above experiment revealed a novel function of the
e
subunit as a coupling
factor of the ATP synthesis reaction. Then, how does the
e
subunit support the highly
coupled ATP synthesis? The
subunit is a small subunit with a molecular mass of
14 kDa and is known to be an endogenous inhibitor of the ATP hydrolysis activity of
F
1
. In the case of bacterial F
1
, its inhibitory effect is reduced in the presence of high
e
