286 



LIGHT AND LIFE 



of glutathione (GSH) . In addition, GSH has been found to help 

 maintain luciferase activity during initial purification steps. 



Regardless of the nucleotide used in the assay system, a large num- 

 ber of metal ions have no effect on the activity of the crude extract 

 at 10-3 jvf concentrations. These include magnesium, manganese, 

 nickel, calcium, cobalt, zinc, molybdenum, and iron. Although metal 

 ions have no effect on the crude extract, chelating agents such as 

 Versene are potent inhibitors (Table 3). Regardless of the nucleotide 

 used in the test system, the inhibitory action of Versene requires 

 approximately 15 minutes incubation with the test system to reach 

 a maximum level. The addition of magnesium ions, in amounts in 

 excess of that of Versene, does not reverse the inhibition. Thus, 

 Versene inhibition cannot be explained simply in terms of binding 

 one of these metal ions. 



In the absence of phosphate, zinc ion is a potent inhibitor of 

 luminescence. Under these conditions, for example, luminescence 

 is completely inhibited at 2 X 10""^ ^ zinc ion. The lack of zinc 

 inhibition in phosphate buffer is due to the fact that an insoluble 

 zinc phosphate forms at the pH used in the assay system. 



Although the luminous bacteria and sea pansies discussed here are 

 both marine organisms, the properties of the enzymes involved in 

 the two luminescent systems differ considerably in their response 



1800 



u u u ATP 



10 15 20 25 30 35 40 



TIME (min.) 

 rig. 8. Comparison of tlu- kiiiclits using (lillcuut miclcotidcs. 



