[lu I L IBRARY 



THE LIGHT-INDUCED ELECTRON SPIN RESONANCE 



SIGNALS OBSERVED IN THE GREEN BACTERIUM 



CHLOROPSEUDOMONAS ETHYLICUM^ 



CHRISTIAAN SYBESMA and JOHN J. HEISE 



Biology Departme)it, Brookhaven National Laboratory 

 and The Charles F. Kettering Research Laboratory 



Photosynthetic activity in a variety of organisms seems to be 

 correlated with unpaired electrons generated by light. These unpaired 

 electrons have been observed by electron spin resonance absorption 

 (ESR) (1-9,13). In higher plant and algal systems the light-induced 

 ESR consists of two signals, one narrow and fast decaying {n,f: signal 

 I) with a g-value of ca, 2.002 and no hyperfine structure, and one 

 broader and slow decaying {b,s: signal U) with a g-value of ca. 2.005 

 and a specific hyperfine structure (2,3). Rhodospirilluni rubrurn and 

 other purple photosynthetic bacteria produce only one ;?,/ signal which 

 has no hyperfine structure (3) and a g-value of 2.003 (4) or 2.002 (5). 

 While the origin of the b,s signal is not yet determined (the O2 evolv- 

 ing system has been implicated (6), as well as the CO2 fixing system 

 (4)), there have been suggestions as to the origin of the «,/ signal. 

 Calvin and collaborators (4,7,8) indicated that in higher plant, algal, 

 and bacterial systems the signal is generated by unpaired electrons 

 in photogenerated positive chlorophyll radicals in the environment 

 of a cytochrome. More specifically, Beinert, Kok and Hoch (9) have 

 presented evidence that in the green alga Anacystis uidulans the n,f 

 signal is due to a photooxidized form of the photoconverter "P700," 



In the following paragraphs some preliminary data are given on the 

 light-induced ESR in whole cells of the green photosynthetic bacterium 

 Chloropseudonionas ethylicnni, strain 2K, and in a sonic fraction of 

 these cells. This organism, like the other green bacteria, contains, in 

 addition to the main chlorophyll pigment, chlorobium chlorophyll, a 

 small amount of another chlorophyll, chlorophyll-770, which has a 

 striking resemblance to bacteriochlorophyll (10)2, xhe substantial 



1 The experiments were carried out at the Charles F. Kettering Research Lab- 

 oratory, Yellow Springs, Ohio. Contribution No. 114. 



" Bacteriochlorophyll is the chlorophyll of purple photosynthetic bacteria. 

 Chlorobium chlorophyll-660 (bacterioviridin) is the main chlorophyll in most 

 green bacteria and has maximum absorption at about 740-750 m/i in vivo and 

 at 660 mju in ether solution. Chlorophyll-770 is the minor chlorophyll in green 

 bacteria and has maximum absorption at 809 m/i /;/ vivo and at 771 m/n in 

 ether solution. 



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