CLOSE VICINITY OF LHC B1 AND LHC B4 IN PHOTOSYSTEM-II - MEMBRANE-FRAGMENTS AS VERIFIED BY CHEMICAL CROSS-LINKING

The nearest neighbourhood of pigment-protein complexes within Photosys tem II (PSII) membrane fragments has been studied by means of chemical cross-linking with o-phthalaldehyde (OPA) in conjunction with protein -chemical techniques. By means of OPA-induced cross-linking a major co njugate of about 60 kDa has been identified. This conjugate was shown to consist of two pigment-protein complexes of light-harvesting comple x II (LHC IT), Lhc bl (CP27) and Lhc b4 (CP29) by means of SDS/PAGE in combination with an immunological analysis using mAbs directed agains t Lhc b4 and by matrix-assisted-laser-desorption-ionization mass spect rometry (MALDI-MS) and sequence analysis of peptides derived from a pr oteolytic digest of the conjugate. Domains of Lhc bl and Lhc b4 have b een localized to a distance of not more than 5 Angstrom within LHC TI. Our results are discussed in the light of recent models on the topogr aphy of the two subunits within the antenna system of Photosystem II.