w. D. Mcelroy and j. w. Hastings 193 



reversible complexing of the enzyme luciferase. The evidence suggests 

 that an active intermediate composed of luciferin, luciferase, Mg++, 

 and ATP is first formed, which, in the presence of oxygen, will react 

 to give rise to an excited state that subsequently decomposes to emit 

 a quantum of light. Most of the active intermediate is normally con- 

 verted into an inactive complex which effectively immobihzes the 

 enzyme. Except for oxygen, all the components necessary for light 

 emission are also essential for the complexing process. The formation 

 of the inactive complex is accelerated by Mg++ and by additional 

 luciferase or other proteins, particularly inorganic pyrophosphatase. 

 The level of the low light intensity appears to be a measure of the 

 steady-state equihbrium between active intermediate and inactive 

 complex. Removal of the inorganic pyrophosphatase by various means 

 affects both the basal light intensity level, as well as the rate of decay. 

 The relationship between Mg++ and ATP for maximum lumines- 

 cent activity (Mg++ to ATP ratio of approximately 1) suggests that 

 the true substrate for the formation of the active intermediate with 

 the luciferin-luciferase is a specific Mg-ATP complex. Similar sug- 

 gestions have been made by Hers for liver fructokinase and by Kielley 

 and Kielley for mitochondrial adenosinetriphosphatase (ATPase). The 

 relationships between Mg, inorganic pyrophosphatase, and active 

 intermediate for the formation of the inactive complex indicate a 

 similar type of reaction. The action of inorganic pyrophosphate and 

 triphosphate in stimulating light production, after its initiation by 

 ATP, is attributed to the rapid breakdown of the inactive complex 

 by these agents. In the case of pyrophosphate the evidence shows that 

 it competes with ATP in the formation of the active intermediate. 

 Thus the addition of pyrophosphate before ATP strongly inhibits light 

 emission. The duration and extent of this inhibition depends, however, 

 on the concentration of both pyrophosphate and pyrophosphatase. On 

 the other hand, the delayed addition of pyrophosphate leads to an 

 initial stimulation followed, in many cases, by a decline and then a 

 rise to a secondary peak which rapidly decreases to the baseline level 

 as the pyrophosphate is hydrolyzed by the action of pyrophosphatase. 

 Such results are to be expected if pyrophosphate splits the inactive 

 complex to form initially some active intermediate. The amount of 

 active intermediate formed would depend upon both the nature of the 



