Electron Transport and Oxidative Phosphorylation

Figure 20.27
The binding change mechanism for
ATP synthesis by ATP synthase.
This model assumes that F 1 has
three interacting and
conformationally distinct active sites.
The open (O) conformation is
inactive and has a low affinity for
ligands; the L conformation (with
“loose” affinity for ligands) is also
inactive; the tight (T) conformation is
active and has a high affinity for
ligands. Synthesis of ATP is initiated
(step 1) by binding of ADP and Pi to
an L site. In the second step, an
energy-driven conformational
change converts the L site to a T
conformation and also converts T to
O and O to L. In the third step, ATP
is synthesized at the T site and
released from the O site. Two
additional passes through this cycle
produce two more ATPs and return
the enzyme to its original state.
Garrett and Grisham, Biochemistry, Third Edition