CARTENOIDS OF PHOTOSYNTHETIC BACTERIA 



25 



(XYD) 



a)R=H R*= 

 b)R=CH3 R'=/<OH 



OCH, 



P518 (2-keto-spirilloxanthin) 



The carotenoids OH-Y and OH-R have furthermore been shown to 

 be the major carotenoids of anaerobic and illuminated aerobic cultures 

 respectively, of Rps. gelatinosa, and can, according to recent investi- 

 gations (8,4), presumably be depicted as (XIX) and (I). These two 

 compounds both contain a tertiary methoxyl and a tertiary hydroxyl 

 group and can formally be considered as having arisen from pigment 

 Y (XIV), more recently named spheroidene (28), and spheroidenone 

 (pigment R) (XVI) by a type 3 reaction (23), that is, addition of H2O to 

 an isopropylidene end-group. Hence OH- spheroidene (XIV) and OH- 

 spheroidenone (I) should be successors instead of precursors of 

 spheroidene (XIV) and spheroidenone (XVI). 





H3CO 



W^ Spheroidene (Y) 



3|(XI2) 



W^ OH-Spheroidene(OH-Y) 



(XK) 



Demethylated spheroidene 

 +OH-Y 



KCO 

 OH 0- 



:^OH-R 

 (ID 



31 



Spheroidenone (R) 



cm) 



OH 

 OH- Spheroidenone( OH-R) 

 (I) 



This assumption is supported by recent studies on the carotenoid 

 biosynthesis in Rps. gelatinosa carried out in collaboration with Eim- 

 hjellen (29). The carotenoids of this organism had previously been 

 studied by Goodwin (5). A reinvestigation under more defined condi- 

 tions gave a rather different picture. 



As seen from Table 4, cells grown photosynthetically under 

 anaerobic conditions in light contain spheroidene, OH- spheroidene and 

 spirilloxanthin. These carotenoids are not present in cultures grown in 

 the light with suitable aeration. Instead, the corresponding keto- 

 carotenoids appear in approximately the same relative amounts. The 

 carotenoid complex of semi-aerobic cultures includes all these carot- 

 enoids. Neurosporene is always present at a low concentration in young 

 cultures. 



