Volume 132, number 1 FEBS LETTERS September 1981 THE POLYPEPTIDE COMPOSITION OF THE B850 LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEX FROM RHODOPSEUDOMONAS SPHAEROIDES, R26.1 Edgar DAVIDSON and Richard J. COGDELL Department of Botany, University of Glasgow, Glasgow G12 8QQ, Scotland Received 13 July 1981 1. Introduction In most species of purple photosynthetic bacteria the light-harvesting pigments (bacteriochlorophyll a and carotenoids) are organised into two broad classes of antenna pigment-protein complexes [1-5]. The first class only show a single strong absorption band in the near infiared (NIR), while the second show two strong absorption bands in the NIR. The light-harvest- ing apparatus of wild-type cells of Rhodopseudomo- has sphaeroides is now well characterised and con- tains both of these types of antenna complexes, called B875 and B800-850 (after the respective max- ima of their major NIR bacteriochlorophyll absorp- tion bands) [1,2,4]. However, in contrast, the nature of the major light-harvesting pigment-protein com- plex from the well known carotenoidless-mutant of Rps. sphaeroides R26, has been a matter for specula- tion [6-8]. When R26 was first isolated its long wavelength absorption maximum was at ~870 nm (see, e.g., fig.2 of [9]). It was clear then from both the spectral evi- dence [9] and developmental studies [10] that this represented a carotenoidless B875-type complex. More recently, a number of carotenoidless mutants have been isolated from the closely related species Rps. capsulata [11,12], and again these only contain the B875-type of antenna complex. However, since R26 was first isolated, the strain of R26 used by most laboratories has subtly changed and its long wave- length absorption maximum has moved down to ~855-860 nm (see, e.g., fig.1 of [13]). We have been very fortunate in this study to have been given a vin- tage culture of the original R26 by Professor W. R. Sistrom, which still absorbs maximally at 870 nm. To distinguish between these two strains, we have decided to designate the 'changed' strain as R26.1 and reserve the term R26 for the original 870 nm absorbing strain. In [14] it was shown that at 4 K the long wavelength absorption band of the bacteriochlo- rophyll in whole cells of Rps. sphaeroides R26.1 split into two components. They suggested that R26.1 does in fact contain 2 types of antenna complex. A purified, detergent solubilised antenna complex (B850) has been isolated from Rps. sphaeroides R26.1 [6-8] and is being used in a variety of func- tional studies. It is therefore important to determine which types of antenna complexes are present in membranes from R26.1, and to try and decide which type of antenna complex the isolated B850 represents. Here we have compared the polypeptide composi- tion of chromatophores from R26, R26.1 and wild- type cells. We show below that R26.1 membranes contain the polypeptides from both the B875, and B800-850-types of antenna complex, and that the B850 pigment-protein complex represents an altered B800-850-type of antenna complex. In [8] we had considered that the B850 complex was an altered B875 antenna type. This, however, was incorrect and we now agree with [6,7,15] that the B850 from R26.1 is a B800-850 antenna-type. 2. Materials and methods Cells of Rps, sphaeroides strains 2:4:1 (wild-type), R26 (obtained from Professor W. R. Sistrom ) and R26.1 were grown anaerobically in the light with suc- cinate as the sole carbon source. The cells were har- vested, washed in 20 mM Tris-HC1 (pH 8.0) and dis- rupted by passage through a French pressure cell at 10 tons. in-2. Chromatophores were then isolated from the broken cells by differential centrifugation [ 16]. The B800-850 light-harvesting pigment-protein Published by Elsevier/North-Holland Biomedical Press 00145793/81/0000-0000]$02.50 © 1981 Federation of European Biochemical Societies 81