9V9 



LIGHT AND LIFE 



>- 



CO 



Ld 

 > 



UJ 



3 - 





 3 5 



[LH,] > [E] 



1.5 2 



45 5 55 



SECONDS 



Fig 2. Light emission response to ATI'. The initial rapid decay with a half- 

 time of 0.25 seconds represents product inhibition. The slower decay after the 

 first few seconds, with a half-life of 13 seconds, represents a partial reversal of 

 the inhibition by pyrophosphate and ATP. See text for details. 



The iiii])ortancc of pyroi)hosj)hatc in maintaining this .sustained 

 but inhibited level of luminescence was first observed during the 

 early purification of luciferase (II). The evidence indicated that 

 in the presence of inorganic pyrophosphatase the light response to 

 ATP decreased in a few .seconds to a very low level (Fig. 3) . An 

 extensive series of investigations has shown that the nature of this 

 response definitely dciJcnds ui^on the quantity of inorganic pyro- 

 phosphatase pre.sent in the luciferase preparation (15, 16). If highly 

 purified inorganic pyrophosphatase is added to the luciferin-luciferase 



