Interactions between thylakoid electron transfer complexes. II. Modification studies with glutaraldehyde.

Photosystem I (PSI) and photosystem II (PSII) complexes have been isolated from stacked spinach thylakoid membranes that had been treated with varying amounts of glutaraldehyde. The concentrations of cytochrome f, Q, and P700 have been determined by spectrophotometric methods. It was found that at low concentrations of glutaraldehyde, the amount of cytochrome f associated with either PSII or PSI increased significantly while the amounts of Q and P700 stayed relatively constant. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting analyses indicated the presence of cytochrome f and other components of the cytochrome b6-f complex in the PSII and PSI preparations after glutaraldehyde treatment, but no intermolecular cross-linked polypeptides could be detected. Solubilization of the cytochrome b6-f complex was also inhibited after thylakoid membranes were treated with low concentrations of glutaraldehyde. These results are discussed in relation to current models for the organization of the membrane complexes, and relate to the location of the cytochrome b6-f complex in appressed and nonappressed membrane regions of thylakoids.