FAST LIGHT REACTION 



201 



potential of about 200 mv., which may not be correct. However, there is a broad 

 band at 550; and, if we had been more careful in isolating the pigment, we could 

 have sharpened the band. 



James Smith : The question has been asked about the positions of the bacterio- 

 chlorophyll and bacteriopheoph_ytin absorption bands in the middle of their 

 spectra. In ether the positions of the bands, in m^u, and their specific absorption 

 coefficients (given in parentheses), are as follows: bacteriochlorophyll 577(22.9), 

 530(3.0), 591.5(52.8); bacteriopheophytin 525(31.9), 495(6.5), 384.5(70.6). As 

 we know, the absorption bands maj'^ lie at other positions in living organisms. 



+ AD 0.140 r 



ot 

 550 m;u 



0.120 - 



0100 ■ 



0.080 - 



060 



0.040 



0.020 



5min. 

 light 



20 



40 



120 



140 



160 



180 



60 80 100 



TIME ^MINUTES) 



Fig. 6. Dark reduction and light oxidation of mammalian cytochrome c by 

 cell-free preparations of Rhodospirillum rubnim showing the phenomenon of 

 accelerated dark reduction after a period of illumination. 



Frenkel: (comments added in proof): I would like to add some observations on 

 the ability of cell-free preparations of Rhodospirillum ruhrum to reduce added 

 cytochrome c in the dark and on the phenomenon of accelerated dark reduction of 

 cytochrome c after illumination of this system. Cell-free preparations in 0.2 M 

 glj'cylglycine buffer (pH 7.5) with an optical density of 0.3 at 800 m/i are placed 

 in Thunberg tubcis with or without mammalian cytochrome c (0.5 n^l in a final 

 volume of 3.0 ml,) which are then evacuated. In Fig. 6 above, slope A is the initial 

 rate of dark reduction of cj^tochrome (1.4 X 10~' optical density unit per 

 minute at 550 m^u). After 80 minutes in the dark, the tubes are illuminated with in- 

 candescent light for 5 minutes, which brings about oxidation of the added cyto- 



