W. D. MCKLROY AND J. \V. HASTINGS 



83 



level (7). If crystalline inorganic pyrophosphatase is added to the reaction mix- 

 ture the baseline light intensity is greatly depressed. The rate of decay to the 

 baseline level is likewise greater. Such a reaction, containing pyrophosphatase, 

 is shown in ligure 4. The decline of luminescence after its initiation with ATP to 

 the low baseline level is due to a reversible inactivation or inhibition of lucif erase. 

 As shown in figure 4, additional lucif erase added secondarily to the reaction 

 mi.xture gives a response very similar to the initial reaction, indicating the pres- 



TIME - MINUTES 



Fig. 4. Luminescent response to the successive addition of luciferase. The reaction mixture 

 contains luciferin and ATP. Additional o.i ml of partially purified luciferase was added at the 

 times indicated. At 12 minutes o.i ml of inorganic triphosphate was added (final concentration, 

 0.00 1 m) (6). 



ence of adequate substrates and cofactors. As reported previously, the second- 

 ary addition of pyrophosphate to such a reaction mi.xture will give a flash 

 m rise time less than 0.1 sec.) whose rate of decay depends upon the concen- 

 tration of pyrophosphatase. 



We believe that pyrophosphate functions in stimulating luminescence by 

 removing an inhibitor from the enzyme surface. Additional details concerning 

 this action of pyrophosphate have been discussed elsewhere (7). Within the 

 photogenic cell w^e believe that the reactive intermediate is present, but is held 



