On the Time Sequence of Reactions in the Anaerobic 

 Light Effect in Rhodo spirillum rubrum* 



BRITTON CHANCE, Johnson Research Foundation, University of Penn- 

 sylvania, Philadelphia, Pennsylvania 



The possibility of participation of the cytochrome d in the photo- 

 synthetic activity of Rhodo spirillum rubrum was suggested by 

 Duysen's spectroscopic recordings (1). We were later able to show 

 with more accurate recordings that several cytochrome or cyto- 

 chrome-like pigments were affected when the anaerobic bacteria 

 were illuminated with infrared light; we identified absorption bands 

 attributable to cytochromes of types c^, b, and a "CO-binding pig- 

 ment" that can act as a terminal oxidase in several bacteria (2,3). 

 It was further shown that oxygen causes spectroscopic effects that are 

 nearl}^ identical to those caused by infrared illumination. This led us 

 to suggest a mechanism for the light effect shown which proposes, 

 among other things, that the oxidizing equivalents produced by the 

 photochemical reaction affect a chain of enzymes, which are very 

 similar or identical to those that are affected by oxygen. 



If this mechanism is correct and the oxidizing equivalents react 

 with the chain at the level of the terminal oxidase, then a time se- 

 quence along the respiratory chain should be recorded upon illumina- 

 tion of the anaerobic cells. Duysens (1) found the spectroscopic 

 changes to be complete in a time of the order of a second. We already 

 noted that the reaction kinetics, at various wavelengths, were di- 

 phasic and that the 430 m^u component responded most rapidly to 

 illumination (2). In the meantime, Olson (4) found that the spec- 

 troscopic effects following infrared illumination of Chromatium oc- 

 curred in two distinct phases, and has included in this volume the 

 spectra of the components involved in the rapid and slow effects. 



Although the reactions in R. rubrum are much more rapid, it has 

 been possible to record at low temperature the spectra corresponding 

 to slow and rapid reactions by means of a sensitive spectrophotom- 



* This research is supported in part by the National Science Foundation. 



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