54 E. F. MACNICHOL, JR. 



phosphatase is very potent, the light intensity is depressed proportionally to 

 the amount of protein that is added. One can add enough protein to the system 

 to bring the intensity down to the order of one or two per cent of the initial 

 light intensity. This system will continue to luminesce for hours. If one adds 

 inorganic pyrophosphate to the system, one obtains a flash of light the dura- 

 tion of which depends upon the rate of hydrolysis of pyrophosphate. If a very 

 small amount of pyrophosphate is added with a high concentration of pyro- 

 phosphatase, one gets a spark of light and if this is recorded on a cathode ray 

 oscillograph you get a typical flash which is super-imposable on the normal 

 firefly's flash. 



Chairman Gerard: Of what duration? 



Dr. McElroy: On the order of two seconds, in this case. This is an example 

 of how one can depress enzymatic activity, i.e., hold it at a low, steady state 

 level with all the elements there that are necessary for light emission. If one 

 puts in a stimulant, if you want to call adding pyrophosphate a stimulus, a 

 response is observed which is identical to that of the firefly. There is only one 

 other way you can obtain the flash in this system and that is by placing the 

 system under anaerobic conditions and then letting in oxygen. Under these 

 conditions one obtains a flash but it is about ten times too long in duration. 

 We have been unable at present to obtain a very rapid flash by this procedure. 

 We have one hypothesis which fits an awful lot of data collected from this 

 system. It is now clear that the ATP reacts with luciferin to form an active 

 luciferin and pyrophosphate. The active luciferin in the presence of oxygen is 

 oxidized and is converted eventually into an excited molecule. This excited 

 molecule then decomposes into oxyluciferin, adenylic acid and light. Oxylucif- 

 erin turns out to be a potent inhibitor of luciferase as far as light emission is 

 concerned. However, oxyluciferin, itself, can react with ATP to form pyro- 

 phosphate and presumably adenyl-oxyluciferin, the latter being the competitor 

 with active luciferin for the luciferase. Pyrophosphatase depresses the light 

 intensity by favoring the formation of the inhibitor while the latter pyrophos- 

 phate stimulates luminescence by removal of the inhibitor. 



I could go into more details and supporting evidence for this but I think it 

 is enough to show how one can have in a biological system all of the reactants 

 that are necessary for carrying out a process without the event actually occur- 

 ring. It is a charged but depressed system requiring appropriate stimuli to 

 bring it back temporarily to a very active state. 



The addition of inhibitors like calcium which has a very interesting effect on 

 this system, it prolongs the light simply because it inhibits the inorganic pyro- 

 phosphatase action. It might have some analogies with the in vivo systems 

 discussed this morning. 



Dr. Robert Grenell (Psychiatric Institute, University of Maryland): 



