Photooxidation of antenna bacteriochlorophyll in chromatophores from carotenoidless mutant Rhodopseudomonas sphaeroides and the attendant loss of dimeric exciton interaction

Journal Article · Sat Sep 01 00:00:00 EDT 1979 · Proc. Natl. Acad. Sci. U.S.A.; (United States)

DOI:https://doi.org/10.1073/pnas.76.9.4429· OSTI ID:5475086

Rafferty, C N ^[1]; Bolt, J; Sauer, K; Clayton, R K

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1. Cornell Univ., Ithaca, NY

Intense continuous illumination of purified chromatophores from carotenoidless mutant Rhodopseudomonas sphaeroides results in progressive photooxidative loss of the near infrared absorption band near 860 nm assigned to antenna bacteriochlorophyll. The quantum yield of this reaction is low, approximately 1.7 x 10/sup -5/. The loss in near infrared absorption is accompanied by a proportional shift in the absorption maximum to shorter wavelengths. The double circular dichroism feature in the near infrared decreases at a faster rate than does the absorbance. These results are explained by a model in which the antenna bacteriochlorophyll, initially associated as dimers (lambda/sub max/ = 860.2 nm), is progressively converted to the monomeric state (lambda/sub max/ = 851.9 nm). The wavelength shift is attributed to disruption of exciton coupling in the dimer. Acetone/methanol extraction indicates that the maximum molar extinction coefficients of the dimer and monomer do not differ by more than 4%. The occurrence of an absorption maximum at 852 nm for monomeric bacteriochlorophyll in a protein complex demonstrates that it is not necessary to invoke aggregation of the chromophores as the origin of the shift from 770 nm in typical organic solvents.

• OSTI ID: 5475086
• Journal Information: Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 76:9; ISSN PNASA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
550700 -- Microbiology
59 BASIC BIOLOGICAL SCIENCES
BACTERIA
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHLOROPHYLL
DIMERS
ELECTROMAGNETIC RADIATION
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
MICROORGANISMS
MUTANTS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHESIS
PHOTOSYNTHETIC BACTERIA
PHYTOCHROMES
PIGMENTS
PORPHYRINS
RADIATIONS
REACTION KINETICS
RHODOPSEUDOMONAS
SYNTHESIS
TOLERANCE
VISIBLE RADIATION