302 



LIGHT AND LIFE 



fact that the himinescent system is not highly purified, makes it diffi- 

 cuk to ascribe a specific role or importance to each of the above 

 factors. 



Attempts to replace the salt requirement by the addition of trace 

 amounts of various inorganic ions were imsuccessful. Moreover, with 

 extracts centrifuged for 2 hours at 105,000 X g in the Spinco prepara- 

 tive ultracentrifuge, the activity was found exclusively in the super- 

 natant. Thus, the salt effect is not apparently related to an effect 

 upon a particulate system. 



;.^^4)2^°4 



TARTRATE 



FINAL CONCENTRATION - MOLAR 



Fig. 6. The clFcct of various salts upon the initial light intensity in the lumines- 

 cent reaction. Light intensity is expressed in arbitrary units relative to (NH4)oS04, 

 which was taken as 100 at its optimum concentration. The reaction mixture 

 was composed of 0.45 ml of 0.1 M Tris-maleate buffer, pH Q.5, 0.1 ml of 1% 

 crystalline bovine serum albumin, 0.1 ml cold water (.nuyatilax extract, salt, and 

 water to a total volume of 2 ml. The /;H of the salt solutions were adjusted to 

 pH 6. .5 wiiere necessary. Similar results were oi)tained using more concentrated 

 buffer, as well as witli ))artiallv purilied en/vme (Tal)le 1). 



There are at least three possible ways in which salt may be effec- 

 tive in promoting the luminescent reaction. None of these alterna- 

 tives have been excluded at the present lime. First, the salt may act 

 directly upon the enzyme. Alternatively, the luciferin molecule may 

 be modified to an active form in the presence of salt. A third possi- 

 bility is that the quantum yield from the reaction might be increased 

 in the presence of salt, thus implying an effect upon the excited 

 state, L*. 



