ELECTRON TRANSPORT IN R. RUBRUM 



283 



400 



450 500 



WAVELENGTH (m^j) 



550 



600 



Fig. 6. Action spectrum of light-stimulated respiration of "young" light-grown 

 cells of R. nibnon whose light-sensitive respiration had been depressed approx. 

 95 per cent with 0.15 M '^-butanol. The ratio of dark to light respiration was 

 determined to be 2.4. In this experiment, the cell suspension was previously 

 mixed with 0.15 M n-butanol and the assay was carried out under air or a gas 

 mixture of CO : O2 = 4:1. In assay, irradiation by scanning lights (variable in 

 wavelength) was immediately followed by diphasic response under the gas mix- 

 ture containing CO, but monophasic under air. During the time required for 

 arrangements in this assay, the respiration was altered in response to light so 

 that light stimulation was observed. The action spectrum of the light-stimulated 

 respiration thus altered was measured with some experimental difficulties. In 

 assay under the gas mLxture, the null balance between the scanning and control 

 (550 m/i) lights was made for only the initial phase of response. Using air in- 

 stead of the gas mixture gave similar results, but the'response was monobasic 

 (20). Taylor (unpublished) obtained similar action spectra, using cells which 

 were so aged that their respiration was stimulated by light (see text). 



action spectra for light-stimulated respiration with aged cells resemble 

 the absorption spectrum of bacteriochlorophyll treated with ferric 

 chloride or iodine (25). It seems likely that oxidation products of 

 bacteriochlorophyll cause the oxygen uptake stimulated by illumination, 

 Geller and Lipmann (26) have reported that some pigments having 

 peaks between 420 m/z and 435 mfi are reduced when the chromato- 



