ESR SIGNALS IN GREEN BACTERIA 



TABLE 1 



The ESR Signals Produced by Light of Different Wavelengths 

 in Wiole Chloropsetidomonas ethylicum Cells 



355 



Chlorobium 



Chlorophyll 744 10 2.2 x 10l5 0.37 2.002 



(maximum) 



Chlorobium 

 Chlorophyll 703 



1.5 X 10l5 0.43 



2.002 



20 



22 



ing as it was in this case, Calvin (13) and Heise(3) have shown that a 

 totally absorbing sample shifts the ESR signal action spectrum maxi- 

 ma toward longer wavelengths. The layers of bacterial cells near the 

 surface of incidence ofthe light absorb light at the absorption maximum 

 to the extent that other layers are shaded. This results in minimum 

 ESR signals at the absorption maxima. In the case of excitation with 

 825 myu light, however, little or no shading was present, as is indicated 

 by the observation that upon removal of the filters to produce intense 

 white light the signal amplitude does not increase significantly with 

 respect to the amplitude of the signal produced by 825 m/i light. Thus, 

 the relative magnitudes of the ESR signals at 744 m/i and 825 m^ can- 

 not be taken as significant. 



To make a more reasonable comparison, incident light with Amax, 

 703 m/i was used. With less absorption by chlorobium chlorophyll at 

 this wavelength (see Table 1), the production of unpaired electrons 

 should occur through more layers of cells than is the case for light 

 with Xjnax. "^^^ ^^f resulting in less shading. However, it is still im- 

 possible to state how much of the difference in amplitude between the 

 signal produced at 825 m/y and that produced at 703 m/i is due to dif- 

 ferences in shading. Taking into account the difference in quantum 

 intensity at these two wavelengths (Table 1), the conclusion can be 

 made that chlorobium chlorophyll is at least 60% as effective as 

 chlorophyll- 770 in producing unpaired electrons. 



