Pheophytinization of bacteriochlorophyll c and energy transfer in cells of Chlorobium tepidum |
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Authors: | S Tokita Masamitsu Hirota Niels-Ulrik Frigaard Keizo Shimada Katsumi Matsuura |
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Institution: | (1) Department of Biology, Tokyo Metropolitan University, Minamiohsawa 1–1, Hachioji, Tokyo, 192–0397 Japan e-mail: tokita-seiji@c.metro-u.ac.jp Tel.: +81-426-772583; Fax: +81-426-772559, JP |
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Abstract: | Bacteriochlorophyll (BChl) c in whole cells of Chlorobium tepidum grown at 46 °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.
Received: 2 October 1998 / Accepted: 22 April 1999 |
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Keywords: | Bacteriochlorophyll c Bacteriochlorophyll a Bacteriopheophytin c Chlorobium tepidum Chlorosome Energy transfer |
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