282 



ELECTRON TRANSPORT 



Nijenhuis (23). Comparison of the action spectrum with the absorption 

 spectrum indicates that the efficiency of light absorbed by carotenoids 

 is approximately 40 per cent of that absorbed by bacteriochlorophyll, in 

 good agreement with Goedheer (24), 



0.0 



0.2 



0,3 



-0.1 



400 



450 



500 550 



WAVELENGTH (myj) 



600 



0.0 



Fig. 5. Action spectrum of light inhibition on respiration of "young" light- 

 grown cells of R. ntbno)/. Before and after this experiment, it was determined 

 with the use of the oxygen-electrode method that the ratios of dark-to-light 

 respiration were from 1.9 to 2.1 at 27°C. The action spectrum was measured 

 by an apparatus which was devised by Castor and Chance (21). Other experi- 

 mental conditions were the same as for Fig. 1, except that pH of the cell sus- 

 pension was 7.2. The absorption spectrum was measured with a Cary, model 

 14R, spectrophotometer, using a chromatophore suspension prepared by the 

 conventional 90-second sonication method (chromatophores (S)) (20). 



The cells, particularly if aged under aerobic conditions or disrupted, 

 started to show the oxygen uptake which was stimulated under illumi- 

 nation, Taylor (unpublished results) has found that the action spectrum 

 for light- stimulated respiration with the aged, light- grown cells shows 

 peaks between 420 m/i and 430 m/i, much as in Fig. 6. He also obtained 

 an action spectrum with the aged, blue-green mutant (devoid of caro- 

 tenoids) of Rhodopseudonioiias spheroides, which showed a prominent 

 shoulder at 410 m^ on a peak somewhere in the near ultraviolet and a 

 small symmetrical peak at 520 vaid. It may be worth noting that these 



