Next Assignment? In lab time Friday March 27 or in class starting March 27 or March 30? GMO plants? Herbicide resistance Pathogen/herbivore resistance Improving nutrition Making vaccines, other useful biochems Plant/Algal biofuels?

PSI and PSII work together in the “Z-scheme” Light absorbed by PS II makes ATP Light absorbed by PS I makes reducing power

cyclic non-cyclic Ultimate e - sourceNonewater O 2 released?Noyes Terminal e - acceptorNoneNADP+ Form in which energy isATPATP & temporarily capturedNADPH Photosystems requiredPSIPSI & PSII

Z-scheme energetics

PSII Photochemistry 1) LHCII absorbs a photon 2) energy is transferred to P680

PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H + instead of Mg 2+ ) = primary electron acceptor

PSII Photochemistry 3) P680* reduces pheophytin ( chl a with 2 H + instead of Mg 2+ ) = primary electron acceptor charge separation traps the electron

PSII Photochemistry 4) pheophytin reduces PQA (plastoquinone bound to D2) moves electron away from P680 + & closer to stroma

PSII Photochemistry 5) PQA reduces PQB (forms PQB - )

PSII Photochemistry 6) P680 + acquires another electron, and steps 1-4 are repeated

PSII Photochemistry 7) PQA reduces PQB - -> forms PQB 2-

PSII Photochemistry 8) PQB 2- acquires 2 H + from stroma forms PQH 2 (and adds to ∆pH)

PSII Photochemistry 9) PQH2 diffuses within bilayer to cyt b6/f - is replaced within D1 by an oxidized PQ

Photolysis: Making Oxygen 1) P680 + oxidizes tyrZ ( an amino acid of protein D1)

Photolysis: Making Oxygen 2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e - reservoir

Photolysis: Making Oxygen 2) tyrZ + oxidizes one of the Mn atoms in the OEC Mn cluster is an e - reservoir Once 4 Mn are oxidized replace e - by stealing them from 2 H 2 O

Shown experimentally that need 4 flashes/O2

Mn cluster cycles S 0 -> S 4 Reset to S 0 by taking 4 e - from 2 H 2 O

Electron transport from PSII to PSI 1) PQH 2 diffuses to cyt b 6 /f 2) PQH2 reduces cyt b 6 and Fe/S, releases H + in lumen since H + came from stroma, transports 2 H + across membrane (Q cycle)

Electron transport from PSII to PSI 3) Fe/S reduces plastocyanin via cyt f cyt b 6 reduces PQ to form PQ -

Electron transport from PSII to PSI 4) repeat process, Fe/S reduces plastocyanin via cyt f cyt b 6 reduces PQ - to form PQH2

Electron transport from PSII to PSI 4) PC (Cu + ) diffuses to PSI, where it reduces an oxidized P700

Electron transport from PSI to Ferredoxin 1) LHCI absorbs a photon 2) P700* reduces A0 3) e- transport to ferredoxin via A1 & 3 Fe/S proteins

Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase

Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase reduces NADP+

Electron transport from Ferredoxin to NADP+ 2 Ferredoxin reduce NADP reductase reduces NADP+ this also contributes to ∆pH

Overall reaction for the Z-scheme 8 photons + 2 H 2 O + 10 H + stroma + 2 NADP + = 12 H + lumen + 2 NADPH + O 2

Chemiosmotic ATP synthesis PMF mainly due to ∆pH is used to make ATP

Chemiosmotic ATP synthesis PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions

Chemiosmotic ATP synthesis PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions thylakoid lumen pH is < 5 cf stroma pH is 8

Chemiosmotic ATP synthesis PMF mainly due to ∆pH is used to make ATP -> very little membrane potential, due to transport of other ions thylakoid lumen pH is < 5 cf stroma pH is 8  pH is made by ETS, cyclic photophosphorylation,water splitting & NADPH synth

Chemiosmotic ATP synthesis Structure of ATP synthase CF1 head: exposed to stroma CF 0 base: Integral membrane protein

a & b 2 subunits form stator that immobilizes  &  F1 subunits a is also an H + channel c subunits rotate as H + pass through  &  also rotate c,  &  form a rotor

Binding Change mechanism of ATP synthesis H+ translocation through ATP synthase alters affinity of active site for ATP

Binding Change mechanism of ATP synthesis H+ translocation through ATP synthase alters affinity of active site for ATP ADP + Pi bind to  subunit then spontaneously form ATP

Binding Change mechanism of ATP synthesis H+ translocation through ATP synthase alters affinity of active site for ATP ADP + Pi bind to  subunit then spontaneously form ATP ∆G for ADP + Pi = ATP is ~0 role of H+ translocation is to force enzyme to release ATP!

Binding Change mechanism of ATP synthesis 1) H + translocation alters affinity of active site for ATP 2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi due to interaction with the  subunit

Binding Change mechanism of ATP synthesis 1) H + translocation alters affinity of active site for ATP 2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi 3) ATP is synthesized by rotational catalysis g subunit rotates as H + pass through Fo, forces each active site to sequentially adopt the 3 conformations

Evidence supporting chemiosmosis 1) ionophores (uncouplers) 2) can synthesize ATP if create ∆pH a) Jagendorf expt: soak cp in pH 4 in dark, make ATP when transfer to pH 8