198 B. CHANCE, M. BALTSCHEFFSKY, L. SMITH 



Chance : Yes, by hydrosulfite. 



Gafifron: Nobody would really ever expect to get oxygen in Rhodospirillum 

 rubrum. 



Brown : On the right-hand side of Fig. 1 (p. 190) you are removing oxygen from 

 the environment around the cell. Right? 



Chance : Yes. 



Brown : Therefore, the cells can effect the internal change much more rapidly 

 than if they have to use up all the oxygen in the environment as they do on the 

 left? 



Chance : Somewhat more rapidly. 



Brown : You have no evidence, as I see it, that the material penetrates the cell. 



Chance: Our evidence is the fact that the spectroscopic shift is greater with 

 hydrosulfite than with anaerobiosis. 



Brown : That is significant then? 



Chance : The effect is 18% greater with hydrosulfite. With a number of bac- 

 teria hydrosulfite addition reveals pigments that are otherwise not reducible under 

 anaerobiosis. 



Amon : To pursue this point, this is a quantitative change on the right, isn't it? 



Chance : Yes, this is a quantitative change. 



Amon : Could that mean that you have removed the oxygen more completely 

 here in the presence of hydrosulfite? 



Chance : I think we have reduced pigments not reducible under anaerobiosis 

 alone. 



Amon : Will you state the reasons why you don't think the difference could 

 result from the more efficient removal of oxygen on the right and less efficient on 

 the left? 



Chance: The respiratory chain is one of the most efficient oxygen removers 

 known; the reaction has not been shown to be reversible. 



Gaffron : How far apart are the two records in time? I mean, your base line is not 

 dropping. 



Chance : I think this was a couple of minutes. In other words, I shook the sus- 

 pension to oxygenate it and re-establish the oxidized level, which checks very 

 closely. The base line was not dropping. 



Allen: Is there any possibility that the infrared-induced transformation of 

 some of these pigments might be pH-sensitive? 



Chance : We have some data from yeast cells obtained by changing the internal 

 pH. If these cytochromes are like the ones in yeast, a spectral shift is unlikely. 



Allen : Dr. Hendley has found rather large "gushes" of acid on illuminating some 

 strains of purple bacteria. These very much resemble the changes in transmission 

 that you get initially on turning the light on. I wonder whether there is a connec- 

 tion between the gushes and your absorption changes. 



Chance: We would expect a change of pH to affect the pyridine nucleotide 

 because it is in equilibrium with hydrogen ions. In yeast cells we find that the 

 P5Tidine nucleotides are oxidized when acid penetrates the cells, but the cyto- 

 chromes are not oxidized or reduced and thus would not respond spectroscopically 

 to the acid gushes. Unfortunately, we don't get any response at 340 vein with the 



