Localisation of Rhodopseudomonas viridis reaction centre and light harvesting proteins using ferritin-antibody labelling.

Rhodopseudomonas viridis thylakoid membrane polypeptides were characterised by SDS gels, 2 D gels and surface-specific iodination. Four polypeptides with apparent molecular weights of 38 000, 33 000, 27 000, and 24 000 (reaction centre) and three low molecular weight polypeptides 11 000, 8000 and 6000 (probably light harvesting polypeptides) were identified. Antibodies were produced against the polypeptides eluted from SDS gels and tested for specificity by an immunoblotting assay. The antibodies were bound to the membranes and viewed by electron microscopy using a modification of the ferritin labelling technique. It is suggested that antigenic determinants for the 38 000, 33 000, and 27 000 reaction centre polypeptides and the 11 000 and 8000 low molecular weight polypeptides are present on the cytoplasmic membrane surface. The 33 000, 27 000, 11 000 and 6000 polypeptides appear to have surface-located residues which can be iodinated. The photosynthetic membrane of Rps. viridis appears to be a highly asymmetrical membrane.