226 LIGHT AND LIFE 



activating reactions (see Fig. 1) . Competition for E-LHo-AMP by 

 pyrophosphate and by oxygen in the Hght-producing reaction results 

 in a decrease in the initial rate. However, the reaction of pyrophos- 

 phate with E-L-AMP removes the inhibitor from the enzyme sur- 

 face; and the result is an increase in the turnover of the enzyme and 

 a consequent increase in total light production. Magnesium ion in- 

 creases the rate of the reaction between PP and E-LHo-AMP and 

 thereby affords nuich greater competition with the light reaction (20, 



21). ' 



The reversal of these two activating reactions by pyrophosphate has 

 actually been shown by demonstrating a net synthesis of ATP as well 

 as the incorporation of P32-labeled pyrophosphate into ATP. That 

 L-AMP is the inhibitor of luciferase is clearly shown when chemically 

 synthesized L-AMP is added to a light-producing reaction, which is 

 initiated with either LHo and ATP or LHo-AMP. Because of the 

 very tight binding of the oxyluciferyl adenylate to the enzyme, equi- 

 molar amounts of LAMP and enzyme essentially produce no light 



L + ATP + Mg' 



(E)> (L) 



E^L+ATP+ Mg*'*' 



460 m^i. 544 m|x 

 Fig. (i. riiiorcsrciuc of I. ami E-L-AMP. Relative lluorcsccncc is plottcil along llie 

 ordinate and tlie wavelength for emission along tlic abcissa. When excess enzyme 

 is added. I lie iiilcnsc Ihiorescencc at 51 I m^ decreases rapidly. 



