Absorption properties of the carotenoids after alkaline denaturation of the light-harvesting complex II from Ectothiorhodospira sp.

6 p., 4 fig. This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution-NoDerivs 3.0 Germany License, which permits to copy and redistribute the material in any medium or format.Alkaline treatment of the Ectothiorhodospira sp. light harvesting system II induces monomerisation of the bacteriochlorophylls and a bleaching of the carotenoid absorption bands in the visible region. Concomitantly, the maximum of absorption observed around 373 nm shifts towards 354 nm. This shift does not result from the Soret band but from a change of the absorption properties of the carotenoids. Furthermore, these pigments are not modified chemically but the spectral conversion results from environmental changes. It is assumed that the dissociation of the bacteriochlorophylls in alkaline medium is accompanied by a structural reorganisation of the complex which reinforces the interactions between the polypeptides and the carotenoids.The work was supported by the EC contract CT93-0278 and the DGICYT (Grant PB98-1632).Peer reviewe