The action of lipase on chloroplast membranes: II. Polypeptide patterns of bean galactolipase- and phospholipase A2-treated thylakoid membranes

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.

Changes in the binding and inhibitory properties of urea/triazine-type herbicides upon phospholipid and galactolipid depletion in the outer monolayer of thylakoid membranes : Different behaviour of atrazine-susceptible and-resistant biotypes of Solanum nigrum L

The binding characteristics and the inhibitory power of atrazine and DCMU towards uncoupled electron flow activity were studied in acyl lipid-depleted thylakoid membranes from atrazine-susceptible and-resistant biotypes of Solanum nigrum L. For this purpose, phospholipase A2 from Vipera russelli and the lipase from Rhizopus arrhizus were used to obtain a selective lipid class (phospholipids or galactolipids) depletion which was restricted to the outer monolayer. Neither phospholipid nor galactolipid removal affected the dissociation constant and the number of binding sites of atrazine. In contrast, the dissociation constant of DCMU was increased in phospholipid-depleted thylakoid membranes but remained unchanged after galactolipid depletion. The number of DCMU binding sites decreased significantly after both lipase treatments, but only in the resistant biotype. The inhibitory effectiveness of the herbicide was either decreased or increased (to different extents) depending on the lipid class which was removed from the membrane and on the biotype considered. These results are discussed with reference to the possible conformational changes of the 32 kDa herbicide-binding polypeptide occurring after lipase treatments.

The action of lipases on chloroplast membranes. III. The effect of lipid hydrolysis on chlorophyll-protein complexes in thylakoid membranes

Bean thylakoid membranes treated with various lipolytic enzymes (bean galactolipase, phospholipases A2, C, D) showed marked changes in their acyl lipid composition. As a consequence of acyl lipids hydrolysis, destruction of some chlorophyll a-protein complexes (CP1a, CP1, CPa) or monomerization of the oligomeric of light harvesting chlorophyll a/b protein complex (LHCP) was observed. It is concluded that galactolipids and phosphatidylcholine are responsible for the stability of CP1a, CP1 and CPa, respectively. Phosphatidylglycerol and to some extent monogalactosyldiacylglycerol are essential for the stabilization of oligomeric structures of light harvesting chlorophyll a/b protein complex.