Chemistry Reference
In-Depth Information
FIGURE 5.19
Structure of ATP synthase. (From
Berg, Tymoczko, & Stryer, 2002
:
pp. 974.)
catalysis of ATP synthesis. The central stalk consists of the
g
and
3
subunits, and the
g
subunit has a long
a
-helical
coiled coil which extends into the centre of the
a
3
b
3
hexamer. Crucially for the mechanism, this breaks the
symmetry of the
.
On the basis of binding studies, Paul Boyer proposed a binding change mechanism for proton-driven
synthesis of ATP by the enzyme (
Figure 5.20
)
, which implied that the enzyme (in particular the three
a
3
b
3
hexamer, such that each of the catalytic
b
subunits interacts with a different face of
g
subunits)
could exist in three different forms, one which binds ATP with such high affinity (the tight, T form) that it
converts bound ADP and P
i
b
however, it is incapable of releasing the ATP. At the same time, a second
subunit will be in the loose, L, conformation, which can bind ADP and P
i
, but cannot release them, while the
to ATP
e
