Kinetics of plastoquinol oxidation by the Q-cycle in leaves.
Biochim Biophys Acta
; 1857(6): 819-30, 2016 Jun.
Article
in En
| MEDLINE
| ID: mdl-27056771
ABSTRACT
Electrochromic shift measurements confirmed that the Q-cycle operated in sunflower leaves. The slow temporarily increasing post-pulse phase was recorded, when ATP synthase was inactivated in the dark and plastoquinol (PQH(2)) oxidation was initiated by a short pulse of far-red light (FRL). During illumination by red light, the Q-cycle-supported proton arrival at the lumen and departure via ATP synthase were simultaneous, precluding extreme build-up of the membrane potential. To investigate the kinetics of the Q-cycle, less than one PQH(2) per cytochrome b(6)f (Cyt b(6)f) were reduced by illuminating the leaf with strong light pulses or single-turnover Xe flashes. The post-pulse rate of oxidation of these PQH2 molecules was recorded via the rate of reduction of plastocyanin (PC(+)) and P700(+), monitored at 810 and 950 nm. The PSII-reduced PQH(2) molecules were oxidized with multi-phase overall kinetics, τ(d)=1, τ(p)=5.6 and τ(s)=16 ms (22 °C). We conclude that τ(d) characterizes PSII processes and diffusion, τ(p) is the bifurcated oxidation of the primary quinol and τ(s) is the Q-cycle-involving reduction of the secondary quinol at the n-site, its transport to the p-site, and bifurcated oxidation there. The extraordinary slow kinetics of the Q-cycle may be related to the still unsolved mechanism of the "photosynthetic control."
Key words
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Plant Proteins
/
Plastocyanin
/
Plastoquinone
/
Plant Leaves
/
Cytochrome b6f Complex
Language:
En
Journal:
Biochim Biophys Acta
Year:
2016
Document type:
Article