Abstract
The charge separation and excited states of antenna bacteriochlorophyll in membrane fragments of the recently discovered photosynthetic bacterium Heliobacterium chlorum were studied by absorbance-difference spectroscopy. Formation of singlet excited states of bacteriochlorophyll g with a lifetime of 200 ps or less was observed as the disappearance of the ground state absorption bands. From the absorbance-difference spectra, it was concluded that the primary photochemical reaction consists of the transfer of an electron from the primary donor P-798 to a possibly bacteriochlorophyll c-like pigment absorbing at 670 nm. Electron transfer to the secondary acceptor occurred with a time constant of about 500 ps. The midpoint potential of this acceptor (between -450 and -560 mV) and the absence of significant absorbance changes in the near-infrared upon its reduction suggest that this acceptor is an iron-sulfur center. It is concluded that the primary photochemistry of H. chlorum is similar to that of green sulfur bacteria.
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