In inside‐out vesicles, a large difference is observed in oxygen yield activity between pH 6.5 and 7.6 which is in contrast to right‐side‐out vesicles. The light saturation behaviour of the ...transition S2 → S3 also shows a pH dependence. In inside‐out thylakoids, at pH 6.5, the light saturation curve of the S2 → S3 transitions exhibits 2 different light saturation processes whereas at pH 7.6 it resembles the light saturation behaviour of the other S‐state transitions. This result is explained by the existence of a second donor in the S2 state (different from the main donor), which contributes to about 30% of the S2 → S3 transitions at pH 6.5. This second donor needs to be protonated and thus, is not active at pH 7.6 in inside‐out thylakoids.
In inside-out vesicles, a large difference is observed in oxygen yield activity between pH 6.5 and 7.6 which is in contrast to right-side-out vesicles. The light saturation behaviour of the ...transition S sub(2) arrow right S sub(3) also shows a pH dependence. In inside-out thylakoids, at pH 6.5, the light saturation curve of the S sub(2) arrow right S sub(3) transitions exhibits 2 different light saturation whereas at pH 7.6 it resembles the light saturation behaviour of the other S-state transitions. This result is explained by the existence of a second donor in the S sub(2) state (different from the main donor), which contributes to about 30% of the S sub(2) arrow right S sub(3) transitions at pH 6.5. This second donor needs to be protonated and thus, is not active at pH 7.6 in inside-out thylakoids.
In inside-out vesicles, a large difference is observed in oxygen yield activity between pH 6.5 and 7.6 which is in contrast to right-side-out vesicles. The light saturation behaviour of the ...transition S
2 → S
3 also shows a pH dependence. In inside-out thylakoids, at pH 6.5, the light saturation curve of the S
2 → S
3 transitions exhibits 2 different light saturation processes whereas at pH 7.6 it resembles the light saturation behaviour of the other S-state transitions. This result is explained by the existence of a second donor in the S
2 state (different from the main donor), which contributes to about 30% of the S
2 → S
3 transitions at pH 6.5. This second donor needs to be protonated and thus, is not active at pH 7.6 in inside-out thylakoids.
From Emerson enhancement measurements of O
2 evolution in
Chlorella pyrenoidosa, it was possible to establish a relationship between the concentration of photosystem II open reaction centers (E) and ...the distribution of photons between photosystems I and II
(1 − α)
α
during steady state. The superposition of lights of two different wavelengths (1 and 2) gives concentrations of E and α intermediate between those obtained with light 1 and 2 separately. This relationship extends a previous one based on quantum yield measurements. It has been expressed here by a curve corresponding to a fixed value of the intersystem apparent equilibrium constant (
K). Up to 700 nm,
K remains equal to 6. Above this wavelength, although the margin of error is rather great,
K apparently increases to 12 or more.
The possibility of “spill-over” of light absorbed by System II to System I was studied. There is no probability that this spill-over, if any, exceeds 25% in Chlorella.
The apparent equilibrium constant is decreased by 3(3,4-dichlorophenyl)-1,1-dimethylurea. This is not in favor of the hypothesis of fully independent electron-transfer chains in photosynthesis; it is therefore likely that some communication between those chains exists.
PDF
