Reconstitution of highly purified P700-chlorophyll a protein complexes into galactosyldiacylglycerol liposomes.

Abstract

Reconstitution of highly purified P700-chlorophyll a protein complexes into the chloroplast lipid vesicles and their kinetic properties have been studied. All four major chloroplast lipids, monogalactosyldiacyl-, digalactosyldiacyl-, sulfoquinovosyldiacyl-, and phosphatidyl-glycerol, which were purified from spinach leaves, were found to form liposomes in the presence of 20% (w/w) phosphatidylcholine and function as a barrier against small molecules such as ascorbate and potassium ferricyanide. Plastocyanin, added to the preformed reaction center-liposomes, reduced up to 90% of photooxidized P700 in the P700-chlorophyll a protein complexes, which suggests that the portion of P700-chlorophyll a protein complexes which accomodate the transfer of electrons from plastocyanin is exposed predominantly on the exterior of the vesicles. The effects of cations on the electron transfer from plastocyanin to photooxidized P700 in the reconstituted system were similar to that in the solution system, which suggests the importance of local charges proximal to P700 in the P700-chlorophyll a protein complexes and a minor role of lipid membrane on the effects of cations in the reaction.