Download Chapter 18 Oxidative phosphorylation and photophosphorylation

Synthesizing
ATP
The binding-change
mechanism
or rotational catalysis
(Paul Boyer, 1980s)
Each  subunit
will take three
different conformations
in turn during each
cycle of action.
Releasing
ATP
Binding
ADP + Pi
Synthesizing
ATP
The binding-change
Mechanism
or rotational catalysis
(Paul Boyer, 1980s)
T
Binding L
ADP + Pi
O
The three 
subunits exist
in different
conformations
(T, L or O) at
each moment.
Releasing
ATP
O
L
T
O
L
T
The binding-change
model was elegantly
supported by two
recent experimental
observations.
The three  subunits
of F1 indeed assume
three different
conformations
X-ray crystallography


 subunit

John Walker, 1994
Fluorescence microscopy
Direct observation
of the rotation of
the  subunit
p299-302.
Recorded rotation of the actin filament using a CCD camera
No rotation if ATP is absent or inhibitors of F1-ATPase
is present!
p299-302.
Model of the action of E. coli ATP synthase:
10-14 protons
the proton gradient
needed for every
drives the rotation
3 ATP
of the c ring using
synthesized.
two half-channels
on the a subunit.
Thus ~ 4 protons
per ATP synthezied
Asp-COO-
Asp-COOH
Protonation/deprotonation of an Asp is believed to be
essential for rotating the c ring and the  subunit.
The rotary motion of the bacterial flagella
is energized directly by the proton
gradient present across the cytoplasmic
membrane.
The proton-motive force is used for
active transport through the inner
membrane of the mitochondria.
Heat is generated
in Brown fat
through the
action of
thermogenin,
an uncoupling
protein:
to produce heat to
maintain body
temperature for
animals in hibernation,
of newly born and
adapting to the cold
(thermogenesis).
Electrons in NADH
generated in cytosol
are shuttled into
mitochondria to
enter the respiratory
chain.
cytosol
Matrix
eadily reversible!
Occurs in liver, kidney and heart
The malate-aspartate
shuttle system
The glycerol-3-phosphate
shuttle system
Occurs in skeletal muscle
and brain
Irreversible
The pathways
leading to ATP
synthesis are
coordinately
regulated.
Pyruvate
oxidation
Interlocking regulation
of all these pathways is
realized by the
relative levels of ATP,
NADH, ADP, AMP, Pi,
and NAD+.
[ATP]/([ADP][Pi])
fluctuates only slightly in
most tissues due to a
coordinated regulation
of all the pathways
leading to ATP
production.
The rate of the respiration
is generally controlled by
the availability of ADP
(“acceptor control”)
No ATP consumption,
No electron flow!
Some respiratory proteins
are encoded by the human
mitochondrial genome
Complexes I, III, and IV
and ATP synthase
are assembled by using
subunits made in both the
cytosol and mitochondria.
Photosynthetic organisms
generate ATP and
NADPH (both are needed
for carbon fixation) via
photophosphorylation, the
first stage of
photosynthesis.
Summary（2张PPT 缺失，以下为老版本的）
• ATP is synthesized using the same strategy in oxidative
phosphorylation and photophosphorylation.
• Electrons collected in NADH and FADH2 are released
(at different entering points) and transported to O2 via
the respiratory chain, which consists of four
multiprotein complexes (I, II, III, and IV) and two
mobile electron carriers (ubiquinone and cytochrome c).
• A proton gradient across the inner membrane of
mitochondria is generated using the electron motive
force generated by electron transferring through the
respiratory chain.
• The order of the many electron carriers on the
respiratory chain have been elucidated via various
studies, including measurements of the standard
reduction potential, oxidation kinetics of the electron
carriers, and effects of various respiratory chain
inhibitors.
• Electron transfer to O2 was found to be coupled to ATP
synthesis from ADP + Pi in isolated mitochondria.
• The chemiosmotic theory explains the coupling of
electron flow and ATP synthesis.
• Isotope exchange experiments revealed that the G`0 for
ATP synthesis on purified F1 is close to zero!
• ATP synthase comprises a proton channel (Fo) and a
ATPase (F1).
• The binding-change model was proposed to explain the
action mechanism of ATP synthase.
• The energy stored in the proton gradient can be used to
do other work.
• Electrons in NADH generated in cytosol is shuttled into
mitochondria to enter the respiratory chain.
• The pathways leading to ATP synthesis is coordinately
regulated.
• Photosynthetic organisms generate ATPs (and NADPH)
via photophosphorylation.
• It took a long time for humans to understand the
chemical process of photosynthesis.
• The major light absorbing pigments on thylakoid
membrane was revealed to be chlorophylls.
• Photons absorbed by many chlorophylls funnel into one
reaction center via exciton transfer.
• Two types of photochemical reaction centers have been
revealed in bacteria.
• Two photosystems (PSII and PSI) work in tandem to
move electrons from H2O to NADP+ in higher plants.
• P680+ in PSII extracts electrons from H2O to form O2
via a Mn-containing oxygen-evolving complex.
• ATP synthesis is driven by the H+ gradient across the
thylakoid membrane, with a higher concentration in the
thylakoid lumen.
• Cyclic electron flow in PSI produces ATP, but not
NADPH and O2
• Compounds other than water are also used as electron
donors in photosynthetic bacteria.
• A single protein in halophilic bacteria,
bacteriorhodopsin, absorbs light and pumps protons