E. NEWTON HARVEY 277 



and keratin), are digested by trypsin, these experiments indicate that 

 luciferin is not a common protein, but they give us no idea of the 

 class to which it belongs. 



Salting Out. 



If crude luciferase solution is saturated with crystals of NaCl at 

 20°C. no precipitate forms but only a shght turbidity appears. The 

 solution filters turbid and luciferase is found unharmed in the fil- 

 trate. Saturation with NaCl is a good method of preserving lucif- 

 erase from the growth of moulds and bacteria. 



One-half saturation with MgS04 also produces a shght turbidity 

 and luciferase is found unharmed in the filtrate. Complete satura- 

 tion with MgS04 produces a fine precipitate, again dissolving in 

 water, which contains considerable luciferase. The opalescent fil- 

 trate also contains some luciferase so that saturated MgS04 precipi- 

 tates luciferase partially but not completely. 



One-half saturation with (NH4)2S04 produces a precipitate which 

 contains very little luciferase after washing with half saturated 

 (NH4)2S04. Most of the luciferase is found in the filtrate. On 

 saturation with (NH4)2S04 an abundant precipitate forms and no 

 luciferase remains in the filtrate. The (NH4)2S04 precipitate dis- 

 solves completely in water and gives a brilliant light if mixed with 

 luciferin. 



If a crude solution of luciferin is saturated with NaCl or half sat- 

 urated with MgS04 or half saturated with (NH4)2S04 no precipitate 

 forms. The luciferin remains in solution. With saturated MgS04 

 the luciferin is partially precipitated; with saturated (NH4)2S04 it 

 is almost completely precipitated, but a small amount of luciferin 

 still remains in the filtrate. The addition of acetic acid to the point 

 where precipitation of the crude luciferin solution is complete (prob- 

 ably a nucleoprotein or mucin is precipitated) and subsequent care- 

 ful saturation with MgS04 or (NH4)2S04 does not completely pre- 

 cipitate the luciferin. 



The above results can be confirmed by adding saturated solutions of 

 NaCl or MgS04 or (NH4)2S04 to dry powdered Cypridince. The 

 powder glows strongly in saturated NaCl which dissolves both lucif- 



