409 Biochimica et Biophysica Acta, 502 (1978) 409--416 © Elsevier/North-Holland Biomedical Press BBA 47509 ANALYSIS OF THE PIGMENT CONTENT OF AN ANTENNA PIGMENT-PROTEIN COMPLEX FROM THREE STRAINS OF RHODOPSEUDOMONAS SPHAEROIDES RICHARD J. COGDELL a,. and ANTONY R. CROFTS b a Department of Botany, Universityof Glasgow, Glasgow G12 8QQ, and b Department of Biochemistry, Medical School, Universityof Bristol, BristolBS8 ITD (U.K.) (Received October 3rd, 1977) Summary The pigment content of a B800-850 light-harvesting pigment-protein com- plex isolated from three different stains of Rhodopseudomonas sphaeroides has been determined. In each case the ratio of carotenoid to bacteriochloro- phyll present is very nearly 1 : 3 an no specificity with regard to carotenoid type was observed. The fourth derivative of the infra-red absorption bands of the complex was determined and it is concluded that the minimal functional unit of B800- 850 complex consists of I carotenoid molecule and three bacteriochlorophyll molecules. The data presented here, together with the previous study of Austin, (Austin, L.A. (1976) Ph.D. Thesis, University of California at Berkeley, Lawrence Berkeley Laboratory Report No. LBL 5512) suggest that the 800 nm absorption band represents one of these bacteriochlorophyll molecules while the remaining two bacteriochlorophylls axe responsible for the 850 nm band. The absorption spectra and circular dichroism spectra of the complexes suggests that their structure has not been greatly altered during the purifi- cation. Introduction There is a division of labour within the photosynthetic unit. Most of the bacteriochlorophylls and carotenoids constitute the light-harvesting antenna and funnel the absorbed radiant energy to the other component, the specialised chlorophylls in the reaction centre, where that energy is "trapped". * To whom requests for reprints should be addressed. Abbreviation: SDS, sodium dodecyl sulphate.