LIGHT REACTIONS IN R. VANNIELII 



435 



RESULTS 



Spectral changes. 



The absorption spectrum changes in the region 400 to 600 m// caused 

 by high intensity far red light are shown in the lower portion of Fig, 1, 

 The trough at 423 m/i and the broad dip around 552 to 555 m// indicate 

 cytochrome oxidation. Our tentative interpretation is that all three 

 cytochromes found in Rhodomicrobiiim (8) are involved: C-550, C-553, 

 and B-563. Overshadowing the cytochrome absorption changes in the 

 region from 450 to 600 m/i are a series of three troughs and three 

 peaks which indicate a shift in the carotenoid absorption bands toward 

 the red. The decrease in carotenoid absorbancy at the usual maxima 

 is about 1 to 2 per cent. The light-induced spectral changes are quite 

 similar in either aerobic or anaerobic suspensions at high intensities. 



Low intensity irradiation gives the results shown in the upper por- 

 tion of Fig. 1. The absorbancy changes due to cytochrome oxidation are 

 an order of magnitude smaller than at high intensity, but the shifts in 

 the carotenoid peaks are not even detectable. The asymmetrical alpha 

 trough at 550 m^ implicates mainly cytochromes C-550 and C-553 with 

 some contribution from B-563. 



Variations with light intensity. 



The marked contrast between the qualitative features of the spectra 

 shown in Fig. 1 indicate the importance of light intensity. In Fig. 2 the 



-I I 



■10 



-8 



LOG INTENSITY IN EINSTEIN cm'^ SEC 



Fig. 2. Light -induced absorbancy changes in anaerobic bacteria versus loga- 

 rithm of light intensity at 0.80 jt/. Change in steady-state cytochrome oxidation 

 in terms of A(A422,5 - ^ \i^'o) ^^r^^sx. ^ ^* Carotenoid change in terms of 



^(^540 - A53o)/Aniax ( )• 



