DISCUSS/()\ 309 



FMN plus iilddiydt' plus oxygen ;uul llu' ;ilclc'liyclc (oud iiHiilioii drops 

 linearly and slowly with linic. 11 you put the en/ynie in this preparation, 

 the aldehyde concentration dr()|)s \ery rapidly and then slows up. So there is 

 no question that the rate of aldehyde utilization is directly correlated with 

 the rate of luminescence. In all cases, the total light emitted is proportional 

 to the amount of aldehyde used. 



Dr. Strehler: ^<)u would expect such a result with many mechanisms you 

 nught ])ropose. 



Dr. McElrov: Well, then you would have to explain to me why this 

 en/yme is acting like an aldehyde oxidase. That is all I am saying, it's an 

 aldehyde oxidase. 



Dr. Porter: I would just like to make a suggestion of how some of these 

 effects of buffers which Dr. McElroy mentioned on spectra and yields might 

 occur. In fact, there is a precedent already from fluorescence. If the pH 

 of the excited state is different from that of the ground state, then the 

 luminescence w^e get comes from another species provided equilibrium is 

 established. Now, equilibrium \ery often is not established. It has to com- 

 pete with the radiation process which goes in 10" seconds. The equilibrium 

 is speeded up by the addition of buffers. And one can, therefore, by adding 

 salts or buffers change the species which is emitting from the original one to 

 the one which is in equilibrium with it at that pH. Therefore, you can 

 change the fluorescence spectrum, and of course, the yield if one of the 

 species is not fluorescent. You can change the yield also by adding buffer. 



Dr. McElrov: I hope I did not bring the salt effect up because, as a 

 matter of fact, in tlie firefly system there is no salt effect in tlie highly 

 purified enzyme except in this con\ersion to tlie red peak. That is very 

 specific for inorganic phosphate. In the case of the bacterial system, once 

 you have it purified then you do not have any salt effect there as far as we 

 can obser\e. In other words, you can go up to 0.01 M sodium chloride or 

 any other salt and you do not change the emission peak or, as far as we 

 can tell, the total light. This is the same for the firefly system. 



Dr. Porter: What about bicarbonate? 



Dr. McElroy: It has no effect. As long as you maintain the pH constant. 



Dr. Porter: What about arsenate? 



Dr. McElrov: Arsenate is an inhibitor, but not on the quantum yield. 



Dr. Arnon: I just have a very brief comment on Dr. McElroy's paper. I 

 think that very often when biochemical evidence is given for photochemical 

 events our colleagues, the physicists and photochemists, subject it to severe 

 and rigid scrutiny and analysis on the basis of yield. They say that certain 

 proposed mechanisms are not probable because the yield is too low. I was 

 particidarly impressed that in Dr. McElroy's work a simple thing such as pH 

 changed yields almost 100",,. I think this is another beautiful example of 

 the innate perversity of biological materials which I would like to bring 

 to the notice of our colleagues here from the physical .sciences. 



Dr. Udenfrieno: The importance of oxygen here lias been stressed previ- 



