| 22. |
- Stefánsson, Hreinn, et al.
(författare)
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Fractionation of the thylakoid membrane from Dunaliella salina – heterogeneity is found in Photosystem I over a broad range of growth irradiance
- 1997
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1320:3, s. 235-246
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Tidskriftsartikel (refereegranskat)abstract
- Thylakoids from the green alga, Dunaliella salina, were fragmented by sonication and the appressed grasna membranes separated from stroma lamellae by partitioning in aqueous two-phase systems. The concentration and antenna size of Photosystem I in the two membrane domains were determined for cultures grown at three different light intensities. Although the antenna size of both PS is decreased with increasing growth irradiance, the antenna size of Photosystem I in the grana was approximately 25-30% greater than the antenna size of Photosystem I in the stroma lamellae. Counter-current distribution analysis of sonicated thylakoids revealed that the amount of stroma lamellae increased whereas the amount of the stacked membranes decreased at higher growth irradiance. The overall decrease in the antenna size of PS I, in D. salina, at higher light intensities can therefore be explained by the combined effect of a decrease in the antenna size of Photosystem I, both in the grana and the stroma lamellae, and a relative increase in the amount of stroma lamellae which has smaller Photosystem I antennae than the Photosystem I centers found in the grana. Light-induced protein phosphorylation increased the relative amount of the stroma lamella fraction. This is interpreted as a result of partial unstacking of the grana. It is suggested that this may be a mechanism for increasing the cyclic electron transport around Photosystem I.
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| 23. |
- Stefánsson, Hreinn, et al.
(författare)
-
Phosphorylation of thylakoids and isolated subthylakoid vesicles derived from different structural domains of the thylakoid membrane from spinach chloroplast
- 1995
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728. ; 1231:3, s. 323-334
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Tidskriftsartikel (refereegranskat)abstract
- (1) Thylakoids from spinach chloroplasts were phosphorylated, fragmented by sonication, and then fractionated by aqueous two-phase partitioning to yield membrane fragments, deriving from different structural domains of the membrane: grana, grana margins, grana core and stroma lamellae. The photochemical activities of PS I and PS II, located in the grana, and PS I and PS II, located in the stroma lamellae, were compared for phosphorylated and control thylakoids. The antenna size (reflected by the Km value) and maximum activity (Vmax) of PS II declined by 19 and 23%, respectively, while for PS II the antenna size and Vmax decreased by 4 and 12%, respectively. No significant changes in antenna size were detected for either grana PS I or stroma lamellae PS I. Counter-current distribution was used for the quantitative separation of grana and stroma lamellae vesicles. Upon phosphorylation, the stroma lamellae fraction increased from 30% to 35% of the total, based on total absorbance at 680 nm. This increase can be explained by partial unstacking of the grana periphery and appressed membranes near the fret regions. Portions of the previously stacked membranes can therefore break and separate with the stroma exposed membrane. In addition, since the grana margins contain PS I (with 40% larger antennae than PS I), which is functionally connected to LHC II, it is to be expected that some of these PS I units will also enter the stroma lamellae fraction and thus help contribute to a lower chlorophyll a/b ratio and a small increase in the average PS I antenna size of the stroma lamellae fraction from phosphorylated thylakoids. It is concluded that the incidence of partial destacking of the grana, which occurs due to the phosphorylation of LHC II and PS II polypeptides, may promote the exposure of the granal PS I centers to the aqueous stroma and increase cyclic electron flow around Photosystem I and thereby ATP production over NADPH production. (2) Subthylakoid vesicles, representing the different structural domains, were also examined for their properties following an incubation in presence of light and ATP. Phosphorylation of membrane proteins including LHC II and PS II associated polypeptides was observed in membrane fractions deriving from the grana lamellae and, to a lesser extent, the grana core. Three unidentified polypeptides of 15, 20 and 22 kDa were the most abundantly labeled polypeptides in the stroma lamellae fraction. No membrane proteins became phospho-labeled in the grana margin fraction.
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