PHOTOCHEMISTRY OF BACTERIOCHLOROPHYLL 401 



Fig. 4. Reversible chemical bleaching of the long wavelength band of 

 chromatophores of RliodospiyiUiim nihruni. The remnant of the 880 m/i 

 band in the oxidised state is shifted about 20 m// towards shorter wave- 

 length. The weak 800 m/i band is stable against oxidation. Although it 

 appears that carotenoid bleaching may be partly reversible also, no 

 definite conclusion can be made about this phenomenon. 



REVERSIBLE PHOTOOXIDATION 



Bacteriochlorophyll dissolved in methanol is very unstable in light. 

 Under uptake of oxygen it "bleaches" within a minute into a compound 

 with an absorption spectrum (Fig, 5) similar to that obtained after 

 bleaching with ferric ions and prolonged standing (Fig. 2). The bac- 

 teriochlorophyll spectrum is restored in the dark by addition of 

 ascorbic acid. This restoration is a slow, temperature-dependent 

 reaction, in striking contrast to the immediate restoration of the 

 spectrum immediately after chemical oxidation (Fig, 1), The restora- 

 tion is not complete; about 10-20 per cent of the bleaching is irre- 



