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Spectral Changes Induced by Alkaline pH and Specific Chemical Modification of Amino Acid Residues in the Light‐Harvesting II Antenna Complex from Ectothiorhodospira sp.
Author(s) -
Buche André,
Picorel Rafael
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb03286.x
Subject(s) - chemistry , absorption band , photochemistry , pigment , bacteriochlorophyll , blueshift , absorption (acoustics) , rhodopseudomonas , antenna (radio) , photosynthesis , optics , materials science , optoelectronics , telecommunications , physics , organic chemistry , computer science , photoluminescence , biochemistry
— The absorption spectrum of the membrane‐bound light‐harvesting (LH)II antenna complex from Ectothiorhodospira sp. has two characteristic near‐infrared bands at 797 (B800 band) and 857 (B850 band) nm. Alkaline pH induced a B850 band blue shift of 17–21 nm depending on experimental conditions. The blue shift was totally reversible when the original experimental conditions were re‐established. No significant effect was observed, however, on the B800 band under the same experimental conditions. The intensity and shape of the pigment circular dichroism signals were maintained with the exception of a blue shift of the signal from the B850 band concomitant with the blue shift of that absorption band. Specific chemical modification of the LHII complex with salicylaldehyde allowed correlation of the alkaline pH effect with the neutralization of a lysine positive charge. We propose that the observed blue shift of the B850 band is due to distortion of the bacteriochlorophyll domain as a consequence of electrostatic and probably hydrogen‐bonding changes but not due to modification of the pigment excitonic interactions within the pigment‐protein complex.