Mild extraction of lipids and pigments from Rhodospirillum rubrum chromatophores

Cyclodextrins: a new tool for the controlled lipid depletion of thylakoid membranes

Cyclodextrins (CDs) have been used in controlled lipid depletion of thylakoid membranes avoiding the use of either detergents or lipolytic enzymes. Spinach thylakoid membranes were first treated with different CDs under various conditions. After removal of the CDs by washing, the amounts of mono-- and digalactosyldiacylglycerol (MGDG and DGDG), sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), protein, pigment and plastoquinone remaining in the membranes were determined. The main results, obtained with alpha-CD and heptakis-(2,6-di-O-methyl)-beta-CD (DM-beta-CD), were as follows. (1)Acyl lipids were removed from thylakoid membranes by both CDs (DM-beta-CD being more efficient than alpha-CD; the extent of removal depended on both CD and chlorophyll concentrations. (2) alpha-CD presented a higher selectivity towards lip classes than did DM-beta-CD, but in both cases the removal order was SQDG > PG > MGDG > DGDG. (3) alpha-CD showed a preference for those lipids containing saturated 16-carbon acyl chains whereas DM-beta-CD was essentially insensitive to the fatty acid composition of the lipids. (4) The protein, chlorophyll and carotenoid contents of thylakoids were not affected by CD treatments. (5) Plastoquinones were removable but in small amounts only and with a low efficiency (DM-beta-CD > alpha-CD). (6) For all lipid classes, the extent of lipid removal was higher at 0 degrees than at 20 degrees C. (7) The presence of MgCl(2) reduced the removal of PG and SQDG but not affect galactolipid depletion levels. (8) Staple lipid depletion levels in thylakoid membranes were reached after 5-10 min of CD treatment at 0 degrees C. (9) Of the four CDs tested, only three (alpha-CD, beta-CD, and DM-beta-CD) promoted lipid depletion whereas one (hydroxypropyl-beta-CD) failed completely to do so. It is concluded that CD-mediated lipid removal provides a valuable and versatile tool to achieve controlled and specific lipid depletions in biological membranes. A few examples of the consequences of a CD-induced lipid depletion on fluorescence and electron transport properties of thylakoids are given to show the usefulness of CDs in the investigation of structure-function relationship in photosynthetic membranes.

Role of lipids in functions of photosynthetic membranes revealed by treatment with lipolytic acyl hydrolase

1. Thylakoid membranes and subchloroplast particles I and II enriched in photosystem I and photosystem II, respectively, were treated with a potato lipolytic acyl hydrolase. 2. In the thylakoid membrane fraction, this treatment inhibited electron flows involving both photosystems and the associated photophosphorylations. However, electron flows involving either photosystem I or photosystem II were still preserved. The treatment of thylakoid membranes by lipolytic acyl hydrolase brought about a temporal convergence of different events such as maximal activity of reduced dichloroindophenol-supported electron flows, complete inhibition of photophosphorylations and electron transport activities through photosystem II + I, onset of the decay N,N,N',N-tetramethyl-rho-phenylenediamine-supported activity of photosystem activity and of the stimulation of photosystem activity (from reduced dichloroindophenol to NADP+ by exogenous plastocyanin. 3. Lipolytic acyl hydrolase catalyzed a limited hydrolysis of each lipid but in a stepwise manner, the galactolipids being attacked before the ionic lipids. The extent of the hydrolysis was not more than 50% for each lipid. Most of the hydrolytic process occurred before any significant change in photochemical activities could be observed. 4. In subchloroplast particles I, a treatment by lipolytic acyl hydrolase did not greatly affect the electron transport whilst lipid hydrolysis was almost complete. 5. In subchloroplast particles II, neither the electron flow activities nor lipid content were significantly altered by lipolytic acyl hydrolase. 6. The sites of lipolytic acyl hydrolase action appeared to be localized between plastoquinones and P700. It is suggested that it is not possible to establish a quantitative and/or temporal correlation between the extent of lipid hydrolysis and the inhibition of photochemical activities. 7. The profile of the hydrolysis of lipids in thylakoid membranes suggests that ionic lipids are less accessible to lipolytic acyl hydrolase than galactolipids.

Labeling of chromatophore membranes and reaction centers from the photosynthetic bacterium Rhodospirillum rubrum with the hydrophobic marker 5-[125I]iodonaphthyl-1-azide

Chromatophores of the photosynthetic bacterium Rhodospirillum rubrum and isolated reaction centers were labeled with the lipophilic membrane marker 5-[125I]iodonaphthyl-1-azide. The two smaller reaction center proteins L and M bind more label than the larger subunit H, a fact supporting the proposed localisation of the 3 subunits obtained with hydrophilic labels. Besides these integral proteins the lipids, among them mainly the pigments and the quinones, are highly labeled suggesting a hydrophobic environment around these molecules and a preferred reactivity to iodonaphthylazide. Such a hydrophobic environment may be of great importance for the function of the photosynthetic reaction centers especially for the charge separation and the primary reactions in electron transport.