Identification of psbA and psbD gene products, D1 and D2, as reaction centre proteins of photosystem 2.

A recent report (Nanba O, Satoh K: Proc. Natl. Acad. Sci. USA 84: 109-112, 1987) described the isolation from spinach of a putative photosystem 2 reaction centre which contained cytochrome b-559 and three other electrophoretically resolvable polypeptide bands, two of which have molecular weights comparable to the D1 and D2 polypeptides. We have used in vivo labelling with radioactive methionine and probed with D1 and D2 monospecific antibodies (raised against synthetically expressed sequences of the psbA and psbD genes) for specific detection of these proteins in a similarly prepared photosystem 2 reaction centre preparation. These techniques identified a 32 000 dalton D1 band, a 30 000 dalton D2 band and a 55 000 dalton D1/D2 aggregate, the latter apparently arising from the detergent treatments employed. Digestions with a lysine-specific protease further confirmed the identification of the lysine-free D1 polypeptide and also confirmed that the D1 molecules in the 55 000 dalton band were in aggregation with other bands and not in self-aggregates. The D1 and D2 polypeptides (including the aggregate) are considerably enriched in the photosystem two reaction centre preparation compared to the other resolved fractions.