Cj. Law et al., ANTENNA ORGANIZATION IN THE PURPLE BACTERIUM RHODOPSEUDOMONAS-ACIDOPHILA STUDIED BY FLUORESCENCE INDUCTION, Photosynthesis research, 52(2), 1997, pp. 157-165
The photosynthetic membrane of the purple bacterium Rhodopseudomonas (
Rps.) acidophila is composed of reaction centers (RCs) which are surro
unded by closely connected light harvesting complexes (LH1) and periph
eral light-harvesting complexes (LH2). Both LH1 and LH2 - which bind t
he antenna pigments between alpha-, beta-heterodimers - form rings com
posed of an integer number of alpha-, beta-subunits. Here we use the s
igmoidicity of fluorescence induction curves to probe the excitonic co
nnectivity of RCs in order to gain information on the structural arran
gement of these LH complexes in the natural chromatophore membrane. Th
e data exclude models of the Rps. acidophila photosynthetic unit that
assume aggregates of RC-LH1 complexes or linear chains of RC-LH1 compl
exes to which LH2 complexes are attached on the periphery. Rather, the
y support the model suggested by Papiz et al. ((1996) Trends in Plant
Science 1:198-206) in which peripheral light-harvesting rings tightly
surround each core complex (LH1-ring with the RC inside) circumferenti
ally.