w. D. Mcelroy and j. w. Hastings 



187 



diate increase in the light intensity which reaches a maximum within 

 a second. The intensity decreases during the next few seconds to a 

 minimum, then begins to rise, and finally reaches a secondary maxi- 

 mum, from which it rapidly decreases to the low baseline level. Ions 

 that are known to inhibit pyrophosphatase activity greatly influence 

 the response to added pyrophosphate. Mn++, in the concentration 

 used, should inhibit the action of pyrophosphatase approximately 90%. 

 The results in Fig. 19 indicate that the light intensity in the presence 



6 8 10 12 14 

 TIME- MINUTES 



18 20 



Fig. 20. The effect of pyrophosphate on the luminescent response to ATP ( McEl- 

 roy et ah, 1953). Sodium pyrophosphate was added initially to reaction mix- 

 tures B, C, D, and E to give a final concentration of 5 X 10 *, 2 X 10 "^ 

 5 X 10 '^ and 10 * respectively. 



of Mn++ is maintained at a high steady-state level for considerable 

 time. Intermediate concentrations of Ca++ and fluoride give similar 

 effects. 



Pyrophosphate in low concentrations is a potent inhibitor of the 

 luminescent reaction if added prior to the ATP. Apparently it can 

 compete with the latter to form an inactive intermediate with the 

 luciferin-lucif erase system. As the results in Fig. 20 indicate, however, 

 this inhibition is slowly reversed if pyrophosphatase is present. The 

 higher the pyrophosphate concentration, the longer is the time re- 

 quired to reach the second peak of luminescence. The quantitative 

 relationships between initial inhibition by various concentrations of 



