bstractSecondary electron transfer

bstract
Secondary electron transfer in photosystem II
(PSII), which occurs when water oxidation is inhibited,
involves redox-active carotenoids (Car), as well as chloro-
phylls (Chl), and cytochrome
b
559
(Cyt
b
559
), and is believed
to play a role in photoprotection. Car
D2
may be the initial
point of secondary electron transfer because it is the closest
cofactor to both P
680
, the initial oxidant, and to Cyt
b
559
, the
terminal secondary electron donor within PSII. In order to
characterize the role of Car
D2
and to determine the effects of
perturbing Car
D2
on both the electron-transfer events and on
the identity of the redox-active cofactors, it is necessary to
vary the properties of Car
D2
selectively without affecting the
ten other Car per PSII. To this end, site-directed mutations
around the binding pocket of Car
D2
(D2-G47W, D2-G47F,
and D2-T50F) have been generated in
Synechocystis
sp. PCC
6803. Characterization by near-IR and EPR spectroscopy
provides the first experimental evidence that Car
D2
is one of
the redox-active carotenoids in PSII. There is a specific
perturbation of the Car
•
?
near-IR spectrum in all three
mutated PSII samples, allowing the assignment of the
spectral signature of Car
D2
•
?
; Car
D2
•
?
exhibits a near-IR peak at
980 nm and is the predominant secondary donor oxidized in
a charge separation at low temperature in ferricyanide-trea-
ted wild-type PSII. The yield of secondary donor radicals is
substantially decreased in PSII complexes isolated from each
mutant. In addition, the kinetics of radical formation are
altered in the mutated PSII samples. These results are con-
sistent with oxidation of Car
D2
being the initial step in sec-
ondary electron transfer. Furthermore, normal light levels
during mutant cell growth perturb the shape of the Chl
•
?
near-IR absorption peak and generate a dark-stable radical
observable in the EPR spectra, indicating a higher suscep-
tibility to photodamage further linking the secondary elec-
tron-transfer pathway to photoprotection

ผลลัพธ์ (อังกฤษ) 2:

Bstract
Secondary Electron Transfer in photosystem II
(PSII), which occurs When Water oxidation is Inhibited,.
involves Redox-Active carotenoids (Car), As Well As Chloro-.
Phylls (Chl), and cytochrome.
B
559
(Cyt
B
559
), and is believed
to Play a role in Photoprotection. Car
D2
May be The Initial
Point of Secondary Electron Transfer The closest Because it is.
CoFactor to Both P
680
, The Initial oxidant, and to Cyt.
B
559
, The
Terminal Secondary Electron donor Within PSII. In Order to
characterize The role of Car
D2
and to Determine The effects of
Perturbing Car
D2
on Both The Electron-Transfer events and on.
The Identity of The Redox-Active cofactors, it is necessary to.
Vary The Properties of Car
D2
Selectively Without affecting The
ten other Car per PSII. To this End, Site-Directed mutations.
Around The binding Pocket of Car
D2
(D2-G47W, D2-G47F,.
and D2-t50f) Have been Generated in.
Synechocystis
SP. PCC
6803. Characterization by near-IR and EPR spectroscopy.
The First Experimental Evidence provides that Car.
D2
is One of
The Redox-Active carotenoids in PSII. There is a Specific
perturbation of The Car
•
?
near-IR Spectrum in all Three.
mutated PSII samples, allowing assignment of The The.
Spectral signature of Car
D2
•
?
; Car
D2
•
?
Exhibits a near-IR Peak at.
980 NM The predominant Secondary donor and is oxidized in.
a charge Separation at Low Temperature in ferricyanide-Trea-.
Ted Wild-type PSII. The yield of Secondary Radicals donor is.
substantially decreased in PSII complexes isolated from each.
Mutant. In addition, The Kinetics of Radical Formation are.
Altered in The mutated PSII samples. These results are con-
Sistent with oxidation of Car
D2
being The Initial Step in Sec-
Ondary Electron Transfer. Furthermore, normal light levels
during Mutant Cell growth perturb The Shape of The Chl.
•
?
near-IR absorption Peak and Generate a Dark-Stable Radical.
observable in The EPR Spectra, Indicating a Higher Suscep-.
Tibility to photodamage Further Linking The Secondary Elec-.
Tron -transfer pathway to photoprotection

ผลลัพธ์ (อังกฤษ) 3:

Bstract
Secondary electron transfer in photosystem II
(PSII), which occurs when water oxidation is inhibited
involves,, Redox-active carotenoids (Car), as well as chloro -
phylls (Chl), and cytochrome



B 559 (Cyt B

), 559 and is believed
to play. A role in photoprotection. Car

may D2 be the initial
point of secondary electron transfer because it is the closest
cofactor. To both P

, 680The initial oxidant and to, Cyt



, B 559 the terminal secondary electron donor within PSII. In order to
characterize the. Role of Car

and D2 to determine the effects of


perturbing Car D2 on both the electron-transfer events and on
the identity. Of the redox-active cofactors it is, necessary to
vary the properties of Car

selectively D2 without affecting the
ten other. Car per PSII To, this end.Site-directed mutations
around the binding pocket of Car

, D2 (D2-G47W D2-G47F
and, D2-T50F) have been generated in

, Synechocystis sp. PCC
6803. Characterization by near-IR and EPR spectroscopy
provides the first experimental evidence that Car


D2 is one of the. Redox-active carotenoids in PSII. There is a specific
perturbation of the Car
-
.
near-IR spectrum in all three
mutated. PSII, samplesAllowing the assignment of the
spectral signature of Car D2
-
.



-
; Car D2?
exhibits a near-IR peak at
980 nm and is. The predominant secondary donor oxidized in
a charge separation at low temperature in ferricyanide-trea -
Ted wild-type, PSII. The yield of secondary donor radicals is
substantially decreased in PSII complexes isolated from each
mutant, In addition.The kinetics of radical formation are
altered in the mutated PSII samples. These results are con -
sistent with oxidation. Of Car

being D2 the initial step in sec -
ondary electron transfer. Furthermore normal light, levels
during mutant cell growth. Perturb the shape of the Chl
-
.
near-IR absorption peak and generate a dark-stable radical
observable in the, EPR spectraIndicating a higher suscep -
tibility to photodamage further linking the secondary elec -
tron-transfer pathway to photoprotection

.