DISCUSSION 307 



of the ctciioplioic. Mtwrniopsi.s. These studies either mean that oxygen does 

 not participate at all, or that it is bound in some form for long periods of 

 time antl is inaccessible to the normal respiratory catalysts. 



Secondly, the possible reversibility of ATP utilization in the luminescence 

 of fireflies, which Dr. AfcElroy alluded to, while not rigorously comparable 

 to the findings reported in our manuscript, bears a resemblance to them in 

 principle. The "cofactors" rcnpiired to reverse the process are. one migiit 

 say, particulates from green plants called chloroplasts. 



Thirdly, whereas it may well be that the scheme for the terminal steps in 

 bacterial luminescence will turn out to be that outlined by Dr. McElroy, I 

 do not i)elieve the present evidence can, as yet, rule out the alternative 

 scheme we presented a numl)er of years ago. 



Our hypothesis is based upon the following observations and concepts: 

 (1) We suggested (on energetic grounds) that two flavin molecules should 

 be required for luminescence. This prediction is consistent with evidence 

 obtained by Dr. McElroy and by Drs. Cormier and Totter. (2) The rate 

 of flavin oxidation, as well as the enzyme affinity for oxygen, are increased 

 by the adtlition of aldehyde. (3) The quantum yield for flavin is greater 

 than 1 per molecule, whereas the aldehyde yield is quite low (about 1 

 quantum per 20-30 molecules) . Since so large a percentage (95-98%) of the 

 aldehyde is oxidized without light emission, it appears to be quite possible 

 that the observed oxidation of aldehyde is incidental to the luminescent 

 reaction (i.e., a side or alternate pathway) and that aldehyde is not used 

 in the actual reactions producing light, but only in certain reactions where 

 light is not evolved. 



The scheme which we still prefer is shown in Figure A. 



Whether the aldehyde operates catalytically could be most rigorously tested 

 by measuring the number of additional moles of O- consumed per mole of 

 aldehyde added in the presence of an excess and regenerating supply of 

 reduced FMN. 



Dr. Racker: Before we let Dr. McElroy get away without asking him any 

 questions, I have one question which maybe either Dr. McElroy or Dr. 

 Strehler can answer. Have you tried to reverse the oxidation of the aldehyde 

 to the acids by putting light in? Dr. McElroy has a lot of time. Have you 

 tried it? 



Dr. McElroy: Well, I would like to add one thing first. We have done 

 experiments over a period of one hour with aldehydes in our preparation 

 where the aldehyde is not used if you flo not add reduced FMN. The only 

 time you use aldehyde in the system, with any combination you want to use, 

 is when light is emitted. The correlation with the light emission and the 

 aldehyde utilization is perfect as far as we can see. It is true that the 

 quantum yield so far has been quite low, but I think that there is no question 

 that this can be improved. The only thing is that under the conditions in 

 which Dr. Cormier and Dr. Totter did the experiment (using crude enzyme 

 preparations) aldehyde utilization takes place much faster than the observed 



