VISUAL RECEPTORS AS BIOLOGICAL TRANSDUCERS 55 



Would you have any suggestions about the relationship of such a system to 

 an in vivo system as far as the time factor is concerned? 



Dr. McElroy: As I say, with the appropriate pyrophosphatase concentra- 

 tion and by our adding pyrophosphate we can get the same time relationship 

 as observed in the intact firefly. 



We have to trace the question back a little further now as to how we get 

 inorganic pyrophosphate formed. One can pick any number of ways of getting 

 it from known biochemical reactions. It is also well known that protein bound 

 pyrophosphate occurs in several different organs and cells. The fact that you 

 get a temperature independence in a lot of these processes may mean merely 

 in this case a liberation of pyrophosphate by some other process. I might add 

 that the rate of decline of luminescence is essentially temperature independent. 

 Now what this has to do with nerve conduction and the type of trigger mech- 

 anism we are talking about this morning is anybody's guess. But I am con- 

 vinced that this is the way the firefly controls its flash and since this is under 

 nervous control, I guess that is the reason I can discuss it. 



I should have made one point; namely, we haven't done the experiments, 

 they would be interesting ones to do, to add smaller amounts of pyrophosphate. 

 One could lower this two seconds if necessary. We were interested in duplicat- 

 ing the system that occurs in the firefly. 



Dr. Leo Abood (University of Illinois) : What Dr. McElroy said in connec- 

 tion with pyrophosphate and pyrophosphatase is extremely interesting in light 

 of some findings we made on frog sciatic nerves. We isolated and characterized 

 inorganic pyrophosphate as well as inorganic pyrophosphatase in frog sciatic 

 nerves and during stimulation of these nerves for periods up to 15 minutes to 

 half an hour, we could observe a considerable increase in the inorganic pyro- 

 phosphate of nerve and by the use of tracers we have been able to find a corre- 

 lation between this increase — that is, the entire turnover of pyrophosphate and 

 the turnover of ATP's, suggesting that there is definitely a relationship between 

 them. Also DPN does seem to increase in turnover during this time and the 

 possibility is that the pyrophosphate may come from DPN and ATP. Now 

 what the significance of that is, we do not know. It certainly is a fact. 



Dr. Morales: As Dr. McElroy knows, I am sure, essentially the same 

 story insofar as pyrophosphate is concerned is repeatable in muscle in thiamine 

 and tetra-acetate. I think that it is a very interesting contribution to the con- 

 trol system, but it leaves open the matter of the energy source. I wonder, in 

 his case, what is the substance that is consumed here? Is it presumably the 

 LH-2? 



Dr. McElroy: The LH-2 is consumed, this you can show, but one must use 

 low concentrations of this substrate. If one makes the LH-2 limiting then you 

 get an ordinary enzyme reaction in which the light eventually goes out due to 



