82 PHYSIOLOGICAL TRIGGERS 



centrations which are below saturation for the luminescent reaction are used 

 to initiate the oxygen flash, the duration of the flash is also greatly increased, 

 but mostly as a result of the longer half-time for decay. In these experiments, 

 therefore, the rise time was dependent primarily upon the rate of mixing and the 

 decay time upon the oxygen concentration at values below saturation for 

 luminescence. These results indicate that the intermediate which accumulates 

 under anaerobic conditions, and which is oxidized with light emission, either 

 contains enzyme as a component of a complex or is non-enzymatically oxidized. 

 Further, the intermediate is a complex in which metal ions (IMg"*^ or iMn++) 

 serve as binding agents. The Mg-i-^" and ]\In++ complexes have slightly different 

 velocity constants in the oxidative reaction. These conclusions are in accord 

 with the finding that oxygen is the only compound whose concentration has any 



Fig. 3. Oxygen flash in vitro. The reaction mixture was placed under anaerobic conditions 

 for 2 minutes. The resulting flash upon the admission of air was recorded. Sweep time, 5 

 seconds. 



effect upon the duration of the flash. Since the velocity constant for the oxida- 

 tion of the intermediate is too large to account for the rate of extinction of light 

 in the normal flash, the normal flash cannot occur by the mechanism suggested 

 by the oxygen flash in vitro. 



An alternative mechanism might involve the removal of o.xygen from the cell 

 at the rate of extinction of the normal flash. This is difficult to believe, however, 

 in view of the precision in the duration of flashes. It is even more difficult to 

 believe that oxygen could be physically introduced into the liquid phase of the 

 cell from the tracheolar gas phase at a rate sul^cient to result in the rapid rise 

 time observed in the normal flash. 



A second type of flash may be obtained /;/ vitro by tlie temporary reversal of 

 inactivated enzyme. When all the components required for light emission are 

 mixed together there is an initial flash of light (j 2 rise time less than o.i sec. at 

 25°C.) whose intensity rapidly decreases within a few seconds to a low baseline 



