84 II. T. WITT 



French: Hill lias l)eeM using purified dyo whicli miikos the (iifferoiire. 



Rabinowitch : It is strange tliat. tiiere slioultl l)e a differeiiee. After all, this is 

 just a different quinone. 



Rosenberg : In the experiments with the very short flashes your photographs of 

 the stationary diagrams on the osoillosoope represented many flashes. Did you 

 ever measure what hajjpens with the first flash? I am wondering whether the 

 absorption changes take some time to appear and whether you need several flashes 

 to produce a steady state. 



Witt: If you measure the first flash, i.e., after a long dark time, the increase 

 of af)sorption and the subsequent decline during the first dark period is greater 

 than after many periods of flashing light. 



Gaffron: Quinone, a strong oxidant, quenches the fluorescence in algae. I 

 suspect that, if the absorption changes found with 2,6-dichlorophenolindophenol 

 are really due to changes in chlorophyll, then one should observe a quenching of 

 the fluorescence by phenolindophenol, comparable to that produced bj' quinone. 



Duysens: I don't think the change at 520 ni/u represents, in Chlorelln, a change 

 in the chlorophyll a molecule because you would expect a decrease of the blue 

 absorption band and also a change in the red absorption band. However, the 

 change at 680 m/x I found was appreciably smaller — if it exists at all — than those 

 at 520 and 475 m/x. 



References 



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817(1941). 



2. Bassham, J. A., and Calvin, M., "Photosynthesis" in Currents in Biochemis- 



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 I., Science, 122, No. 8157, 9 (1955). 

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4. Lundeg&rdh, H., Physiol. Plantarnm, 7, 375 (1954); Duysens, L. N. M., 



Science, 120, 358 (1954); 121, 210 (1955); Nature, 173, 692 (1954) ; Chance, 

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5. Emerson, R., and Arnold, W., /. Gen. Physiol, 15, 391 (1932). 



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