143 



Ellen C. Weaver and Norman I. Bishop 



this "CO2" mutant and the one most like it, Mutant 18, are capable 

 of large shifts in absorption at 525 mjj, if the light period is 

 long enough. Figure 5 demonstrates that the absorption in No. 8 

 is still increasing; even at the end of a flash 0.4 second long. 



LIGHT OFF 



"COj MUTANT NO. 8 



-0.4 sec FLASH 

 50 RUNS 



525 



LIGHT OFF, ^O.isec FLASH 

 ^\^ 100 RUNS 



ttlGHT ON 



Fig. 5 



Comparison of the effect of a 0.1 second flash in a total 

 period of 2 seconds, which produces very little change in 



the 525 mp. absorption, with a O.k second flash (period ^i- seconds) 



which produces a large change. 



The picture is quite different when wild type is subjected to 

 flashes of 0,5 second in length. There is a two phase rise at 

 525 mji; first a very steep one, lasting just over 0.1 second, 

 followed by a slower increase in absorption. Evidently at least 

 two absorption changes, one considerably slower than the other, 

 are taking place. The time course of the ^4-25 vcnx shift, however, 

 remains exponential. If one observes the behavior of a represen- 

 tative "O2" mutant. No. 11, with a 0.5 second flash, the time 

 course is more conplicated (Fig. 6). There is a steep rise, 

 followed by a decay which sets in while the light is still onj 

 further decay takes place when the light is turned off. It is al- 

 most as though some substance present in this mutant was decreas- 

 ing in optical density at 525 ^^^> "but with a slower time course 

 than the positive shift. Possibly this substance does not decay 



