26 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



TABLE 4. 



Carotenoid composition o/ Rhodopseudomonas gelatinosa grown in the light 

 and harvested in the late exponential stage of growth 



* These values are the approximate per cent of total carotenoid. 



Further kinetic studies of the carotenoid content of washed cell 

 suspensions incubated in buffer solution in the light revealed that 

 transformations occurred within the carotenoids present, but no net 

 carotenoid synthesis was observed. We consider the results of such 

 experiments to be support for the interconversions depicted in Fig. 2: 

 under anaerobic conditions from neurosporene and spheroidene to OH- 

 spheroidene and spirilloxanthin, and in aerated cultures from neuro- 

 sporene and spheroidenone to OH- spheroidenone and P518, 



The transformations of spheroidene to spirilloxanthin under ana- 

 erobic conditions thus represent an alternative pathway to spirilloxan- 

 thin. Hitherto, the lycopene pathway (as inR. rubrum) has been con- 

 sidered exclusive. 



ANAEROBIC CONDITIONS 



AEROBIC CONDITIONS 



a) 



neurosporene 



\ 



spheroidene (Y) 



I 



b) OH-spheroidene (OH-Y) 



neurosporene 



\ 



spheroidenone (R) 



■*. OH-spheroidenone (OH-R) 



c) 



spirilloxanthin 



P518 



Fig. 2. Carotenoid interconversions in washed cell suspensions of Rhodopseu- 

 domonas gelatinosa. 



