CAROTENOIDS OF PHOTOSYNTHETIC BACTERIA 



DISTRIBUTION. STRUCTURE AND 



BIOSYNTHESIS 



SYNN0VE LIAAEN JENSEN 



Institute of Organic Chemistry 



The Technical University of Norivay, Trondhcim 



A characteristic feature of all photosynthetic bacteria is their con- 

 tent of yellow to violet carotenoid pigments, which contribute to the 

 spectacular colours occasionally exhibited by the bacterial cell. 



Elegant studies of such bacteria, performed by R, Y, Stanier, L, N. 

 M, Duysens and others, have demonstrated the function of the carote- 

 noids as protectors against photo- oxidation and as auxiliary absorbers 

 of radiant energy for photosynthesis and phototaxis. Other functions 

 have been claimed, but not rigidly proven. Pertinent reviews in this 

 field are available (see, for example, 1,2,3), 



In most of the photosynthetic bacteria the biosynthesis of carotenoids 

 proceeds in such a manner that considerable amounts of intermediates 

 can be isolated in addition to end products. The carotenoids of these 

 organisms therefore represent a unique array of compounds which are 

 biochemically and structurally very closely related. In addition, con- 

 ditions can be created under which otherwise inaccessible intermediates 

 accumulate, and their interconversions can be studied. Mainly for the 

 above reasons investigations on photosynthetic bacteria have con- 

 tributed much to the solution of problems connected with the biosyn- 

 thesis of this class of natural products. 



The number of known carotenoid pigments has increased significantly 

 as a result of study of the pigment complex of such bacteria. Despite 

 the fact that the carotenoids of photosynthetic bacteria are chemically 

 closely related, sufficient variation does occur to make them useful for 

 the characterization of these bacteria. 



The present paper will be limited to recent progress in our know- 

 ledge of the distribution, chemical structure, and biosynthesis of 

 coloured carotenoids of photosynthetic bacteria— a topic which reflects 

 the special interest of the author. I hope the limitation is justified by 

 the rapid and perhaps unexpected expansion of this field during the 

 last few years. Much of the work to be discussed has not yet been pub- 

 lished, although it is in press. 



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