Chemistry Reference
In-Depth Information
FIGURE 5.20
Energy-dependent binding change mechanism for ATP synthesis by proton-translocating ATP synthase. F
1
has three
conformationally distinct interacting
ab
protomers: O, the open conformation, has very low affinity for ligands and is inactive; L has loose
binding for ligands and is catalytically inactive; T has tight binding for ligands and is catalytically active. ATP synthesis proceeds in three steps.
(1) Binding of ADP and P
i
to site L. (2) Energy-dependent conformational change converts binding site L to T, T to O and O to L. (3) Synthesis
of ATP at site T and release of ATP from site O. After two further cycles of this reaction cycle the enzyme returns to its initial state. The energy
that drives the conformational change is transmitted to the catalytic
a
3
b
3
assembly via rotation of the
g3
assembly, represented here by the
centrally located asymmetric object (green). (Adapted from
Voet & Voet, 2004
.)
third subunit is in the open, O conformation. This third subunit can exist in two states
one in which, similar to
the T or L forms, a nucleotide is bound, and a second in which it has a more open conformation and releases the
bound nucleotide. John Walker and his group were in fact able to crystallise the bovine heart F
1
-ATP synthase
with each of the three catalytic subunits in one of the three conformational states (
Figure 5.21
)
, confirming the
e
FIGURE 5.21
The X-ray structure of the F
1
-ATP synthase from bovine heart mitochondria. The
a
,
b
, and
g
subunits are in red, yellow, and
blue respectively. The inset (bottom left) shows the orientation of the subunits in this view. The bar is 20
˚
long. (From
Abrahams, Leslie,
