FAST LIGHT REACTION 197 



this reaction. Interestingly enough, this amount is of the same order 

 of magnitude as the cytochrome content. Some further data obtained, 

 under the conditions of Fig. 3, lead to the possibility that the effect at 

 430 m^ has somewhat different kinetics from that at 385 m^u ; the back 

 reaction at 7° has roughly twice the initial rate of that at 430 m/i. 

 Thus two or more components may be involved, and various hypoth- 

 eses for this interesting effect are still under active consideration. 



Discussion 



Granick : In Fig. 3 (p. 187) you had a 520-Tnfj. band that was going up and down. 

 What was that? 



Chance : I cannot say it is all due to cytochrome, although a part of it may be 

 attributed to the beta bands of cytochromes b and c; there are cytochromes which 

 do have relatively large beta bands, for example, cytochrome 6<. Some might be 

 due to the 520-mM band seen in Chlorella. But, of course, the 520-mM band of 

 Chlorella appears upon illumination, whereas that in R. rubrum disappears and 

 has no related effects at 475 mju. It is unUkely that the effect is due to heat for there 

 is the same amount of heat aerobically and anaerobically, whereas there is no 

 spectroscopic effect aerobically and there is a large spectroscopic effect anaerobi- 

 cally. If heat were the cause of these effects, you would expect the same spectro- 

 scopic effect aerobically as anaerobically. 



Granick: When you add hydrosulfite you reduce the cytochrome at the same 

 time that you remove any oxygen that might be there. Was there something else 

 that showed up by the addition of hydrosulfite? 



Chance : Yes, there was a further reduction of cytochrome at 430 m^. Also this 

 experiment suggests that oxygen is not the oxidant for the light effect. 



Frenkel : How long does this hydrosulfite remain in solution as such? Does it 

 decompose very rapidly? 



Chance : It is fairly stable for the three-minute interval. 



Benson : Does it get into your cells? 



Chance : Fig. 1 (p. 190) indicates that it does. It certainly can cause a larger and 

 more rapid reduction of the cytochromes than the endogenous process. 



Strehler : Did you say the O2 is consumed faster than it can be by the endoge- 

 nous process alone? 



Chance : I compared the slopes of the two traces of Fig. 1 (p. 190) and the 

 reduction is more rapid. 



Strehler : But there is extracellular oxygen they have to consume. 



Gaffron : If you bubble nitrogen through, why do you have to add the hydro- 

 sulfite? 



Chance : We add hydrosulfite to see if light can cause oxidation of cytochromes 

 in the presence of this reducing agent. The hydrosulfite affects pigments that are 

 presumably inside the cell, and therefore should also be able to react with any 

 oxygen produced in the cell. 



Gaffron: What would a little oxygen produced by illumination do? Do you 

 think this would be taken care of completely? 



