ENERGY TRANSFER AND CYTOCHROME OXIDATION 

 IN GREEN BACTERIA 



JOHN M. OLSON and CHRISTIAAN SYBESMA 



Biology Depart>}ie)it, Bvookhaven National Laboratory, 



Upton, Neiv York 



The photosynthetic bacteria consist of two main groups: the purple 

 bacteria and the green bacteria. The pathways of energy transfer in 

 purple bacteria have been elucidated mainly through the efforts of 

 Duysens (1), The light-induced oxidation of cytochrome (s) in purple 

 bacteria is well documented (2-7), and it is now quite well established 

 that energy absorbed by or transferred to bacteriochlorophyll drives 

 photosynthetic electron transfer systems composed of b- and c-type 

 cytochromes (as well as cytochromoids in some instances). The char- 

 acterization of c-type cytochromes from green bacteria has been 

 carried out by Gibson (8), and a new chlorophyll, which is probably 

 bacteriochlorophyll, has been isolated as a protein-chlorophyll com- 

 plex (9). 



In this paper we present evidence that the terminal acceptor of 

 electronic excitation energy in green bacteria is the bacteriochloro- 

 phyll-like chlorophyll-770, and that chlorobium chlorophyll serves as 

 an accessory pigment for efficient collection of light energy. Light- 

 induced oxidation of c-type cytochrome (s) is demonstrated, and the 

 quantum efficiency shown to be comparable to the efficiency of cyto- 

 chrome oxidation in purple bacteria. 



METHODS AND MATERIALS 



Chloropseudomonas ethylicum, strain 2K, and Chlorobium thiosul- 

 fatophilum, strain L, were grown on 0.1 per cent ethanol and 0.1 per 

 cent Na2S203'5H20 respectively (See Appendix). Cps . ethylicum 2K 

 contains chlorobium chlorophyll-660 (10) and C. thiosulfatophilum L 

 contains chlorobium chlorophyll-650 (11). Both also contain a rela- 

 tively small amount of chlorophyll-770. Absorption spectra of whole 

 cell suspensions are given in Appendix, Fig. 5, p. 497. 



Fluorescence emission spectra (dQ/dy) were determined as de- 

 scribed previously (12) and are expressed in quanta cm-2 sec-1 

 sterad"! /i , Total quantum emission was determined from the area 

 under the emission spectrum. 



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