PHOTOCHEMISTRY OF BACTERIOCHLOROPHYLL 403 



The similarity of the absorption spectrum of the compound obtained 

 by a) chemical oxidation and storage in air- saturated solution and b) 

 photobleaching in light in air-saturated solution makes us suggest that 

 the same compound is formed in both processes. This suggestion is 

 supported by the following experiment. 



Addition of ferrous sulfate to the compound mentioned under a) 

 above results in only a weak immediate restoration of the far red ab- 

 sorption band (Fig. 2, insert), while addition of ascorbic acid— which 

 restores the spectrum both in the chemically oxidised system and in 

 the photochemically oxidised system— results in both an immediate and 

 a slow restoration (Fig. 2, insert). In the latter case a much higher 

 percentage of reversibility is obtained. The time course of the "slow 

 component" obtained by chemical bleaching and the time course of 

 reversibility of photobleaching (Fig. 5, insert) are similar; they both 

 depend on temperature in the same way. These results thus strongly 

 suggest that the secondary product obtained with chemical bleaching 

 and the product obtained with photobleaching are the same. 



From this result we would expect that, if oxygen is rigourously 

 excluded, a compound with an absorption spectrum analogous to the 

 one presented in Fig, 1 will occur. Due to the high sensitivity of bac- 

 teriochlorophyll to even traces of oxygen this has not yet been con- 

 firmed with this pigment. The reversible bleaching of chlorophyll in 

 oxygen-free methanol and other solvents, observed by Porret and 

 Rabinowitch (8), Livingston (9) and Linschitz and Rennert (10) might 

 be explained in this way. 



The sequence of events leading to chemical and photobleaching 

 then may be written as follows: 



Chemical bleaching: 



spectrum Fig. 1 

 BChl"^ + ©2 ^BChlO 



spectrum Fig, 2 



Pho toblea ching: 



absorption 

 BChl , BChl' 



fluorescence 



BChl' ^BChl^ + e" 



