Pheophytinization of bacteriochlorophyll c and energy transfer in cells of Chlorobium tepidum.
Bacteriochlorophyll (BChl) c in whole cells of Chlorobium tepidum grown at 46 degrees C changed into bacteriopheophytin (BPhe) c within 10 days after reaching full growth. When a small amount of C. tepidum cells in which BChl c had been completely pheophytinized were transferred to a new culture medium, normal growth was observed after a short lag phase, and the absorption spectrum of the growing cells showed the presence of a normal amount of BChl c. During the growth of C. tepidum in the new culture, the BChl c concentration was nearly proportional to the cell density measured by turbidity (OD640). These results indicate that C. tepidum can survive even when BChl c has been completely pheophytinized and that BChl c is newly synthesized in such cells when transferred to a new culture medium. In partly pheophytinized cells, upon excitation of BPhe c at 550 nm the fluorescence emission spectrum showed maxima at 775 and 810 nm, which correspond to emissions from BChl c and BChl a, respectively. This indicates energy transfer from BPhe c to BChl c and BChl a. In cells in which BChl c was completely pheophytinized, fluorescence measurements were indicative of direct energy transfer from BPhe c to baseplate BChl a. These findings suggest that when BChl c in C. tepidum cells is pheophytinized, the product (BPhe c) remains in the chlorosomes and continues to work as a light-harvesting pigment.
Department of Biology, Tokyo Metropolitan University, Minamiohsawa 1-1, Hachioji, Tokyo, 192-0397 Japan. tokita-seiji@c.metro-u.ac.jp
S
S
Tokita
M
M
Hirota
N U
NU
Frigaard
K
K
Shimada
K
K
Matsuura
D001429:Bacteriochlorophylls / Q000378:metabolism*; D019414:Chlorobi / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D006358:Hot Temperature; D008027:Light; D008274:Magnesium / Q000378:metabolism; D010674:Pheophytins / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D001429:Bacteriochlorophylls; D010674:Pheophytins; D008274:Magnesium