The presence ofphotosystem II polypeptides and photosystem II activity in unstacked regions of barley thylakoid membranes were investigated by immunological and spectroscopic techniques. Immunogold labelling of Lowicryl-embedded chloroplasts showed that PSI and the ATPase were completely excluded from stacked regions, while a significant proportion of PSII was located in unstacked regions of the membrane. A membrane fraction derived from stroma lamellae was shown by immuno-blotting to contain PSII components. Their abundance was approximately one tenth (on a chlorophyll basis) of that in the starting material. The stroma lamellae showed a corresponding level of photosystem If-mediated electron transport, in the presence of the electron donor diphenyl-carbazide. Much of the activity was DCMU insensitive, and the reaction centres lacked the antennae pigment CP29, which was located only in appressed thylakoids. Cytochrome b-559 LP, but not HP, was present in the stroma lamellae fraction. Evidence is presented that the native low potential form ofcytochrome b-559 exists as a unique molecular species, distinct from the high potential form (cytocfirome b-559 HP).

This article summarizes our ultrastructural studies on the organization of the thylakoid membrane of green algae and higher plants. We have used freeze-fracture and immunogold labeling to investigate the lateral distribution of the components in the membrane, their interactions, and the folding of their polypeptide chains in the membrane.

Gold immunolabeling of bovine lens tissue embedded in Lowicryl K4M, using a polyclonal antibody specific for a major component of lens fiber plasma membrane of 26 K molecular weight, shows that this constituent is absent from the epithelial cell plasma membrane and associated only with the junctional and non-junctional domains of the lens fiber plasma membrane.