390 R. LUMRY AND J. D. SPIKES 



Berkeley? The thioctic acid effect seems to be superimposed on tlit; qiiinone effect. 

 The cfTects are additive, on the basis of tlieir own data. 



Spikes: 1 think 1 said ihat tinoctic acid, ghitathione, cystine, and a number of 

 other sulfur-containing compounds will not function as direct Hill reaction oxi- 

 dants in the system, even though they are capable of being rapidly oxidized by 

 manganese dioxide. 



Bassham : I want to ask, in view of the quantum i'e([uirement of the Hill re- 

 action which illustrates transfer of electrons with less than 2 quanta, if you think 

 that the process is sufficiently similar to photosynthesis to take this as an indica- 

 tion that in photosynthesis we also can transfer electrons with less than 2 quanta. 



Lumry: The energy requirements are the same, so draw your own conclusion^. 



Rabinowitch : Do you think that the result obtained with extremelj'^ low concen- 

 tration of oxidants is of importance in connection with Franck's hypothesis that 

 the Hill oxidants associate themselves with chlorophyll? You have so many 

 times fewer molecules of the reductant than of chlorophyll that there would be 

 no chance for reactions based on association. You must have kinetic encounters 

 in order to get a reasonable yield. 



Clendenning : Was your light source white or colored? 



Spikes: It makes no difference whether you do it using an ordinary incandes- 

 cent lamp, so-called white light, or whether you use only a red band with the peak 

 at 675. 



Clendenning : Your effect of concentration will be exacth' the same? 



Spikes: It is possible. We work in a nitrogen atmosphere which cuts down the 

 side effects. Also the blue component of an ordinary incandescent bulb is quite 

 low. There is verj^ little direct photochemical effect even with ordinarj^ white 

 light. 



Brown : We have seen here several effects where the chloroplast reaction seems 

 to behave differently from the photosynthetic in a way which might be considered 

 fundamental. The fact that a much higher saturation rate can sometimes be ob- 

 tained has certain implications, even embarrassing implications. The fact that 

 the ki, for the chloroplast system is sensitive to heavy water, whereas what data 

 we have on the photosynthetic system indicate that an equivalent fci is not sensi- 

 tive to heavy water, also makes one suspect that thei-e may be a basic difference in 

 mechanism. 



Another point which has not been discussed, but which is also fundamental, 

 is the fact that a single flash of light, a very brief flash, that will produce oxygen in 

 the Hill reaction will not produce photosynthesis. 



References 



1. Spikes, J. D., Lumry, R.., Rieske, J. S., and Marcus, R. J., Plant Physiol., 29, 



161-164(1954). 



2. Spikes, J. D., Arch. Biochem. and Biophys., 35, 101-109 (1952). 



3. Bishop, N. I., Lumry, R., and Spikes, J. D., Arch. Biochem. and Biophys., 58, 



1-18 (1955). 



4. Rieske, J. S., Doctoral thesis, University of Utah, Salt Lake City, Utah, 1956. 



