FAST LIGHT REACTION 



193 



Preparation of the materials. The cells were grown as described 

 previously (1). The preparation of the extracts follows as closely as 

 possible the procedures outlined by Frenkel (3). The phosphoryla- 

 tive activity usually corresponded to 22 nM Pyhour for a preparation 

 that gave an optical density reading of 1.0 at 800 m/i. The reactions 

 were carried out in a 0.2 M glycyl-glycine medium of pH 7.4. 



RESULTS 



Phenyl mercuric acetate treatment of whole-cell suspensions. 

 The first indication of the fast light reaction was obtained by a treat- 

 ment of the whole cell suspension of R. ruhrum with 0.1 mM phenyl 

 mercuric acetate (1). The rather complex kinetics of this reaction are 



Fig. 1. The time course of the development of phenyl mercuric acetate inhibi- 

 tor in a suspension of R. ruhrum. The traces also show the effects of infrared illu- 

 mination upon the inhibited cells. 



indicated by the tracing of Fig. 1. The inhibitor is added to the 

 anaerobic cell suspension and, after a 2-minute lag, the reaction 

 that involves a large decrease of optical density at 430 m/x is com- 

 plete. This decrease is caused by an oxidation of cytochromes as the 

 dehydrogenase activity is inhibited; and, as previous studies showed, 

 considerably more cytochrome Co is oxidized under these conditions 

 (1). Infrared illumination causes an abrupt increase of absorption 

 followed by a much slower reaction and the same sequence of reac- 

 tions is recorded when the light is turned off. The spectrum corre- 

 sponding to the fast phase of the light reaction is plotted in Fig. 

 2 and consists of a sharp peak at 430 ni/z* and a trough at 385 m/z. 



* One of us (L. Smith) has restudied this effect and obtains a much broader peak 

 at 432 to 436 m/n. 



