LIGHT-INDUCED AND DARK STEPS OF BACTERIAL 

 PHOTO PHOSPHORYLATION 



MITSUO NISHIMURA 



Joluisoii Researcli Foundation , University of Pennsylvania. Philadelphia 



and Department of Biophysics and Biochei)iistry, Faeulty of Science, 



Unircrsitv of Tokyo, Tokyo 



INTRODUCTION 



The analysis of light- induced and oxygen- activated absorption 

 changes in purple bacteria (1-9) and studies of heme proteins isolated 

 from these organisms (10-17) have indicated that several electron 

 transfer catalysts are functioning in light- and oxygen- activated 

 oxidation- reduction systems. If photophosphorylation is coupled with 

 the oxidation- reduction reactions between these electron carriers, 

 there should exist at least two distinct phases in the process of photo- 

 phosphorylation, namely, a light-induced primary step and light- 

 independent dark processes (electron transfer and ATP synthesis). 



The flashing light technique has been effective in studying the 

 kinetics of photophosphorylation and distinguishing between the primary 

 light-induced step and the dark processes. By this technique, it was 

 observed that photophosphorylation took place in the dark after short, 

 flashing illumination. This "delayed" process of photophosphorylation 

 was affected by certain reagents and temperature. Analysis of the 

 delayed photophosphorylation, combined with spectroscopic studies of 

 the cytochrome system, revealed the presence of two steps in the 

 delayed photophosphorylation; viz., electron transfer and coupled 

 phosphorylation. 



When the dark periods between flashes are sufficiently long, the 

 amount of delayed photophosphorylation per flash is indicative of the 

 amount of substance reacting during the flash. The maximal amount 

 of the delayed process per flash is unaffected by temperature or 

 chemical reagents. From the maximal amount of delayed photophos- 

 phorylation observed, a value of two was suggested as the tentative 

 number of ATP molecules formed per electron transfer in the 

 oxidation- reduction chain. The comparison of relative quantum effi- 

 ciencies in the presence of inhibitors and an activator (MPM) is also 

 suggestive of two phosphorylating sites. Some of the data in this 

 paper have been published (18-20), 



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