Investigation of the effects of different carotenoids on the absorption and CD signals of light harvesting 1 complexes.
Absorption and circular dichroism (CD) spectra of light-harvesting (LH)1 complexes from the purple bacteria Rhodobacter (Rba.) sphaeroides and Rhodospirillum (Rsp.) rubrum are presented. The complexes exhibit very low intensity, highly nonconservative, near-infrared (NIR) CD spectra. Absorption and CD spectra from several mutant and reconstituted LH1 complexes, with the carotenoid neurosporene and the precursor phytoene replacing the wild-type (WT) carotenoids, are also examined. The experiments show that the position of the carotenoid bands as well as the bacteriochlorophyll (BChl)/carotenoid ratio affect the NIR CD spectra: bluer bands and larger ratios make the NIR CD signal more conservative. Modeling results that support this finding are presented. This study, combined with the theoretical approach of the companion paper, where modeling of such complexes is presented and discussed in detail, provide a complete explanation of the origin of the nonconservative NIR CD spectra of LH1 and B820.
Department of Biophysics and Physics of Complex Systems, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands.
Sofia
S
Georgakopoulou
Gert
G
van der Zwan
John D
JD
Olsen
C Neil
CN
Hunter
Robert A
RA
Niederman
Rienk
R
van Grondelle
D000042:Absorption; D002338:Carotenoids / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D002942:Circular Dichroism / Q000379:methods*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008956:Models, Chemical; D045322:Photosynthetic Reaction Center Complex Proteins; D012242:Rhodobacter sphaeroides / Q000378:metabolism; D012246:Rhodospirillum / Q000378:metabolism; D012247:Rhodospirillum rubrum / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared; D013696:Temperature
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002338:Carotenoids