FAST LIGHT REACTION 



195 



though the effect upon the latter is considerably greater. Thus the 

 430 m;u peak is not due to a direct excitation of chlorophyll. 



Studies of extracts of R. ruhrum. Light effects observed in extracts 

 of R. ruhrum prepared as described here are shown in Fig. 4. 

 Without any additions to the extract, the light effect is similar to that 

 recorded in Fig. 3 for the whole cells treated with phenyl mer- 

 curic acetate. Starting at the left-hand side of the record, a rapid in- 

 crease in absorption at 430 myu occurs when the suspension is illumi- 



I50;jM 

 on DPNH 



340-374m>j 



430- 470m;j 



log lo/I ^0.005 

 TT 



Increased O.D. at 

 430nT>j<i, 



Fig. 4. The effects of infrared illumi- 

 nation upon an extract of R. rubrum 

 prepared according to Frenkel (3). 



33>jM 

 DPNH 



Fig. 5. The effect of infrared illumi- 

 nation upon the kinetics of DPNH 

 utilization by an extract of R. rubrum. 

 An increase of optical density at 340 

 m/i corresponds to an upward deflection. 



nated, and a rapid decrease to the original base Hne is observed in 

 other experiments when the light is turned off. The peak of the 

 difference spectrum for this effect lies at a slightly longer wavelength 

 than that recorded in Fig. 2, but the general nature of the effect is very 

 similar. 



If now a reducing agent such as DPNH is added, a large increase of 

 optical density is recorded. The peak of the difference spectrum for 

 the changes caused by DPNH addition is about 428 m^u. This is 

 the expected value corresponding to the reduction by DPNH of the 

 pigment that Kamen has isolated from R. rubrum and shown to be 

 reducible by DPNH (4). This pigment is probably identical with the 

 terminal oxidase that we term the "CO-binding pigment" (5). Infra- 

 red illumination now causes a further rapid increase of absorption, 



