MILTON J. CORMIER 287 



to salt. For example, salts such as NaCl and KCl inhibit the lumines- 

 cence system ol" Roiilla. The inhibition increases linearly with in- 

 creasing salt concentration, 50 per cent inhibition being reached at 

 approximately 2 X '^^~' -^'^ salt. The luminescence of extracts of 

 luminous bacteria, on the other hand, is stinudated by increasing 

 salt concentrations, reaching a maximum steady state at approxi- 

 mately 1.7 X 10-^ M salt (16) . 



Kinetic Data 



Although freshly prepared crude extracts usually do not show 

 significant differences in kinetics between AMP, ADP, and ATP, 

 differences in these kinetics do present themselves when extracts 

 are used that have been repeatedly precipitated two to three times 

 with ammonium sulfate. The latter enzyme preparation, for example, 

 shows large differences in ATP versus ADP or AMP kinetics. Fig. 8 

 illustrates the results of such an experiment. ADP and AMP kinetics 

 are essentially identical, under these conditions, requiring 3.3 minutes 

 to reach half maximum velocity, whereas the response to ATP is 

 much slower, shows a lag period, and requires approximately 17 

 minutes to reach half maximum velocity. 



In addition to observing kinetic differences with the nucleotides 

 tested, this enzyme preparation also requires a metallic ion activator 

 for ATP, but not for ADP or AMP, activity. Ions of magnesium 

 and manganese are among the best activators, but nickel, cobalt, and 

 calcium ions also show considerable activity. The kinetic experi- 

 ments described abo\'e were therefore done in the presence of mag- 

 nesium ion. None of these metal ions has any effect on ADP- or 

 AMP-stimulated luminescent reactions. These results, using mag- 

 nesium ion as an activator, are presented in Table 4. It is of in- 



TABLE 4 



Effect of Magnesium Ion on Luminescence in the 

 Presence of Various Nucleotides 



Additions Relative Light Intensity 



None 69 



ATP 34 



ATP + magnesium 320 



ADP 360 



ADP + magnesium 360 



AMP 380 



AMP + magnesium 380 



Conditions: Same as described under assay system, except that 5 /zmoles of MgCl2 

 were added where indicated and the enzyme used was that described in the text. 



