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



molecules that become transformed? Are these changes of sufficient magnitude? 

 I don't know. 



Rabinowitch : You want to see the changes in the pigments responsible for the 

 changes of absorption; but if you don't know the absorption coefficient of your 

 pigment you just cannot separate the product into two factors. Therefore, you 

 don't know if you have a very small change of the whole material or if a very small 

 part of the material is transformed into something which has a quite different 

 absorption coefficient. 



Lucile Smith : Let us say, if the changes that Dr. Duysens gets and possibly 

 the change observed in the extract of Rhodospirillum are changes in chlorophyll, 

 and if you assume that the Soret peak of chlorophyll is similar to that of cyto- 

 chromes in that region, there are the changes of the same order of magnitude as 

 the changes in cytochromes. 



Duysens: The changes are only 1% of the absorption of bacteriochlorophyll. 

 I think what Dr. Allen wants to ask is whether there is a change of all bacterio- 

 chlorophyll molecules or a change in only a fraction of the bacteriochlorophyll 

 molecules which is very large. At present this question cannot be answered with 

 certainty. 



Brown : There is a related question. That is, if you attempt to compute potential 

 changes from these spectral differences and you calculate for the total quantity 

 of material present, the change might be very small. If you calculate on the basis 

 of assumed compartmentalization the change can be enormous. I don't think 

 there is any easy way out of that dilemma. 



Wassink : Just a comment on this. Under normal light intensities only a small 

 fraction of the chlorophyll will be excited at a certain moment, and you cannot 

 assume that in the presence of an acceptor it stays in the excited stage. 



Rabinowitch: Not in the excited, but in the chemically changed state, yes. 



Wassink : Can you? 



Rabinowitch : Yes, why not? It depends on the lifetime. 



Kamen : Dr. Vernon and I isolated the pigment which is presumably identified 

 with the Rhodospirillum rubrum. It turned out to have a broad band. The region 

 at 550 mju, rather than that at 570 mju, was associated with the 428 m/u peak. It 

 seems to me, therefore, that there should probably not be an anomaly here, at 

 least so far as this is concerned. But it is a broad band and not sharp. It could be 

 that the fast component that you observed, or that the portion of the band at 

 550 m/i which was fast, could have come from this broad band. You would not see 

 it so easily with the resolution of the apparatus now, but I don't think there is any 

 real anomaly. The hemoproteins in these bacteria are not identical with the 

 classical hemoproteins. Any arguments based on what you would expect from the 

 classical type of oxidase need not be of concern to us now. 



Chance: On the other hand, surely there would be a sharp 550 band due to 

 cytochrome c. 



Kamen : And there is. 



Chance : You also state that the 428 might have a broad alpha band. 



Kamen : It does have a broad alpha band in the isolated pigment. I don't deny 

 that in the course of the isolation of this pigment we may have changed it con- 

 siderably because we used rather drastic methods. This can also explain the 



