Aa. Moskalenko et al., STRUCTURAL PECULIARITIES AND CONFORMATIONAL TRANSITIONS OF THE B800-850 COMPLEX FROM CHROMATIUM-MINUTISSIMUM, Biochemistry, 61(3), 1996, pp. 318-325
Effects of various agents (detergents, solvents, salts, etc.) on the s
pectral characteristics (conformational transitions) of light-harvesti
ng B800-850 complex from the purple sulfur photosynthetic bacterium Ch
romatium minutissimum were studied. It was determined that the complex
comprises two dimeric bacteriochlorophylls: long- and short-wavelengt
h. Changing the electrostatic and hydrophobic interactions inside the
complex affects only the long-wavelength dimer of bacteriochlorophyll,
this being revealed as a hypsochromic shift of the long-wavelength ab
sorption band from 855 to 815-845 nm. This is accompanied by a corresp
onding shift in the fluorescence emission band and decreasing circular
dichroism (CD) signal in this region, while the state of both the sho
rt-wavelength dimer (absorption band at 800 nm) and carotenoids do not
change significantly. The effect is fully reversible, e.g., after the
agent is removed, the previous state of the complex is restored. It i
s supposed that a native conformation of the B800-850 complex is essen
tial for its interactions with other complexes. The B800-850/B880-RC a
ssociate was isolated from Chromatium minutissimum membranes under con
ditions stabilizing the native conformation of the B800-850 complex. A
model is discussed describing the observed conformational changes of
the B800-850 complex, the role of the pigments in the stabilization of
its structure, and the regulation of energy transfer from the periphe
ral antenna to the reaction center via this changes.