The bindingchange mechanism or rotational catalysis Paul Boyer

The binding-change mechanism or rotational catalysis (Paul Boyer, 1980 s) Synthesizing ATP Each subunit will take three different conformations in turn during each cycle of action. Releasing ATP Binding ADP + Pi

The binding-change Mechanism or rotational catalysis (Paul Boyer, 1980 s) Binding ADP + Pi Synthesizing ATP T L O The three subunits exist in different conformations (T, L or O) at each moment. Releasing ATP O L T L O T

The binding-change model was elegantly supported by two recent experimental observations.

The three subunits of F 1 indeed assume three different conformations X-ray crystallography subunit John Walker, 1994

Fluorescence microscopy Direct observation of the rotation of the subunit p 299 -302.

Recorded rotation of the actin filament using a CCD camera No rotation if ATP is absent or inhibitors of F 1 -ATPase is present! p 299 -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 FADH 2 are released (at different entering points) and transported to O 2 via the respiratory chain, which consists of four multiprotein complexes (I, 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 O 2 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 F 1 is close to zero!

• ATP synthase comprises a proton channel (Fo) and a ATPase (F 1). • 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 H 2 O to NADP+ in higher plants. • P 680+ in PSII extracts electrons from H 2 O to form O 2 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 O 2 • 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