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3 Mechanism of Unidirectional Rotation of γ Subunit in F 1 -ATPase
α
β
β
α
α
β
ATP
ATP
H 2 O
Pi
γ
Open
Structure
Closed
Structure
Closed
Structure
Fig. 3.6 Structure of catalytic dwell state of α 3 β 3 γ complex stabilized in aqueous solution of ATP,
ADP, and Pi. “ATP• • •H 2 O” represents ATP just before the hydrolysis reaction (i.e., the activated
complex)
α
β
β
α
α
β
ATP
Pi
γ
ATP
ATP
H 2 O
Pi
ATP H 2 O
α
β
β
α
α
β
ATP
ATP
γ
ATP
ATP
ATP
ATP
ATP
H 2 O
Pi
ATP
H 2 O
Pi
(a)
(b)
α
β
β
α
α
β
γ
α
β
β
α
α
β
γ
Fig. 3.7 a Binding of ATP, ATP, and Pi to three β subunits in aqueous solution of ATP, ADP, and
Pi. ATP is bound to a β subunit as ATP• • •H 2 O (see the caption for Fig. 3.6). b Binding of ATP,
ATP, and ATP to the three β subunits in aqueous solution of ATP, ADP, and Pi
nonuniform binding of nucleotides to the three β subunits but also the structural
asymmetry of the γ subunit. It is probable that the packing structure of the α 3 β 3
complex is determined primarily by the packing structures of the three β subunits.
We emphatically remark that the packing efficiency in a β subunit is intimately related
to the chemical compound (i.e., ATP• • •H 2 O, ATP, ADP + Pi, nothing, or Pi) bound