Intermolecular Relations of the Photosystem II Complex in Spinach Chloroplasts as Detected by Immunochemical Assay1

Abstract

Polyclonal antibodies were prepared to the subunits of the spinach photosystem II fraction (PS II): p47, p43, p27, p33, p24, and pl7. (The protein nomenclature refers to M_r). p47 and p43 are the subunits of reaction center complex, and p27 is light-harvesting chlorophyll protein. p33, p24, and pl7 are extractable from PS II with 1 M Tris, and p24 and pl7 with 1 M NaCl. With untreated PS II fractions, the antibody to p24 inhibited the photosynthetic oxygen-evolving activity, but not the DCPI-photoreduction activity in the presence of DPC, indicating that p24 played an important role in the former activity. Bindings of the respective antibodies to the PS II treated with sodium dodecyl sulfate were regarded as 100%. To untreated PS II, the bindings were 20–30% for p47, p43, and p27, about 50% for p33, and 70–80% for p24 and pl7. To NaCl-washed PS n, the binding to p33 increased by 9%, indicating that p33 was adjacent or bound with p24 or/and p17. To Tris-washed PS n, the binding to p43 increased by 7%, indicating that p43 was adjacent or bound with p33. To PS II treated with 3% of Brij 58, only the binding to p27 increased appreciably. To PS II treated with 1% of octyl glucoside, the binding to p47 was still lower than 50%, whereas those to the other subunits were 74–91 %. These values could be a measure of the extents to which the subunits were exposed to the aqueous phase, because of the nature of polyclonal antibodies. These results suggest that in intact PS n, p47, p43, and p27 were in most part buried in the inside, p47 being located at the most central and p27 at the outermost part, whereas p33, p24, and pl7 were exposed to the outside by 50–75%.