Antenna organization in green photosynthetic bacteria. 2. Excitation transfer in detached and membrane-bound chlorosomes from Chloroflexus aurantiacus
The photosynthetic antenna of Chloroflexus aurantiacus includes bacteriochlorophyll (BChl) c/sub 740/ and BChl a/sub 292/, both of which occur in chlorosomes, and B808-866 (containing BChl a/sub 808/ and BChl a/sub 866/), which is membrane-located (subscripts refer to near-infrared absorption maxima in vivo). BChl a/sub 792/ is thought to mediate excitation transfer from BChl c/sub 740/ to BChl a/sub 808/. Lifetimes of fluorescence from BChl c/sub 792/ and BChl a/sub 792/ were measured in isolated and membrane-bound chlorosomes in order to study energy transfer from these pigments. In both preparations, the lifetime of BChl c/sub 740/ fluorescence was at or below the instrumental limit of temporal resolution (about 30-50 ps), implying extremely fast excitation transfer from this pigment. Attempts to disrupt excitation transfer from BChl c/sub 740/, either by conversion of part of this pigment to a monomeric form absorbing at 671 nm or by partial destruction of BChl a/sub 792/ by oxidation with K/sub 3/Fe(CN)/sub 6/, had no discernible effects on the lifetime of BChl c/sub 740/ fluorescence. Most of the fluorescence from BChl a/sub 792/ decayed with a lifetime of 93 +/- 21 ps in membrane-attached chlorosomes and 155 +/- 22 ps in isolated chlorosomes at room temperature. Assuming that the only difference between these preparations is the occurrence of excitation transfer from BChl a/sub 792/ to B808-866, a 41% efficiency was calculated for this process. These results imply either that BChl a/sub 792/ is not an obligatory intermediate in energy transfer from BChl c/sub 7/$/sub 0/ to B808-866 or (more probably) that chlorosome isolation introduces new processes for quenching fluorescence from BChl a/sub 792/.
- Research Organization:
- Arizona State Univ., Tempe (USA)
- OSTI ID:
- 5405901
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 26:26; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
ABSORPTION SPECTRA
CARBOXYLIC ACIDS
CHLOROPHYLL
EMISSION SPECTRA
FLUORESCENCE
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
LUMINESCENCE
MOLECULAR STRUCTURE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOSYNTHETIC BACTERIA
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
SPECTRA