Biomedical Engineering Reference
Fig. 2 Schematic representation of the structure of F 0 F 1 -ATP synthase. See text for details.
Reproduced by permission from Balzani et al. 2003
and inorganic phosphate, P i . When F 1 dominates, it hydrolyzes ATP and drives the
F 0 motor in reverse, turning it into an ion pump that moves ions across the mem-
brane against the electrochemical gradient. The mechanochemistry of ATP synthase
has been studied in great detail (Boyer 1993 ; Rastogi and Girvin 1999 ; Stock et al.
1999 ; Oster and Wang 2000 ; Ren and Allison 2000 ; Seelert et al. 2000 ; Bustamante
et al. 2001 ; Frey 2002 ; 2003 ; Schliwa and Woehlke 2003 ) and new structural infor-
mation continues to appear (Rondelez et al. 2005 ) .
This enzyme consists of two principal domains (Fig. 2 ). The asymmetric mem-
brane-spanning F 0 portion contains a proton channel, and the soluble F 1 portion
contains three catalytic sites which cooperate in the synthetic reactions. The cata-
lytic region is made up of nine protein subunits with the stoichiometry 3 a :3 b :1 g :1 d :1 e ,
approximating to a fl attened sphere, 10 nm across and 8 nm high. The fl ow of pro-
tons through F 0 generates a torque, which is transmitted to F 1 by an asymmetric
shaft, the g-subunit. This subunit acts as a rotating “cam” within F 1 , sequentially
releasing ATPs from the three active sites. The free energy difference across the
inner membrane of mitochondria and bacteria is suffi cient to produce 3 ATPs per 12
protons passing through the motor.
As mentioned above, the F 0 F 1 -ATP synthase is reversible, i.e., the full enzyme
can synthesize or hydrolyze ATP; F 1 in isolation, however, can only hydrolyze it. The
spinning of F 1 -ATP synthase, i.e., the rotary motor nature of this enzyme, was fi rst