324 A. H. KRALL 



there but there is no excitation so that you get the absorption but not a fluores- 

 cence yield? 



Emerson : Wlien we did this work we thought we had abundant evidence that 

 the absorption was there and photosynthesis was not. But I must say that I plan 

 to look at this again and under better conditions. The absorption was dropping 

 very rapidl}- and it was necessary to take increasing quantities of cells to maintain 

 approximately the totality of the absorption as we went further into the infrared. 

 I still think that the yield drops very rapidly in this region. Just how it drops I 

 think is subject to modifications. 



Wassink: Well, my original intention was to make a comment on the dark in- 

 activation of photosynthesis. I think we long ago produced considerable evidence 

 that there is an effect of oxygen on non-photochemical parts of the system. You 

 can demonstrate that for instance by making repeated exposures, say, of 5 or 10 

 seconds. We have done that with diatoms and with Chlorella. We have published 

 it for diatoms not for Chlorella, but it is essentially the same. 



After the short dark periods the quantum efficiency is the same as in continuous 

 light, whereas the saturation level is nmch reduced. The latter is reached at lower 

 light intensities. It is restored to the normal level in a period of something over 10 

 seconds. Also we found that it is connected with a drop in the fluorescence yield 

 which is due to a shift toward the more oxidized condition. So it is very likely 

 that, indeed, oxygen, or at least oxidized compounds, are responsible for restora- 

 tion of full activity. I mean this is the same as you envisage. 



I don't know, of course, how CO comes in there. I think the CO effect overlaps 

 this and inactivates the thing completely in the absence of light. 



Smith : Dr. Yocum many years ago found that carbon monoxide inhibits chloro- 

 phyll accumulation, not the transformation of protochlorophyll to chlorophjdl, 

 but the making of more chlorophyll after the initial transformation. I don't know 

 how this fits in. 



Granick: I should like to make a comment on Kamen's suggestion that cyto- 

 chrome apparently needs some kind of an absorption band a little further toward 

 the red than chlorophyll. We do know of such a thing. A long time ago. Dr. IMc- 

 Kalish with a Beckman photometer found bands in the infrared for various sub- 

 stances like sodium iodide, sodium chloride, and water. Testing substances like 

 hemoglobin he picked up what was a small band, it is true, somewhere around 700. 

 That was for oxyhemoglobin, and he tried methemoglobin, fluoride, and a few 

 others. There are very thin bands out in that region. The physical chemists call 

 them forbidden bands. Whether they are forbidden or not they are there. 



The question arises whether traces of absorption of this character might pos- 

 sibly be used, say, in the transfer of energy from one pigment to another. I don't 

 know, but it is very interesting to know that thej^ are there. 



Strehler: First, in defense of Dr. Kamen, I don't think that it is absolutely 

 necessary that any energy receiving pigments, e.g., cytochromes, have an absorp- 

 tion band in the region beyond or overlapping chloroph^yll fluorescence if they are 

 bound to or closely associated with a chlorophyll molecule. In this case the combina- 

 tion of the two pigment molecules might well shift the chlorophyll absorption band 

 to the red far enough that the complex might itself be a sink for light energy 

 through sensitized transfer. Then, since the cytochrome itself would be in direct 



