E. NEWTON HARVEY 285 



is present in considerable excess, as on addition of an equal volume 

 of saturated aqueous picric acid. Further addition of a little dilute 

 acetic acid or HCl does not cause precipitation. The solution filters 

 turbid and luciferin may be demonstrated in the filtrate on adding 

 luciferase. A yellow light due to the picric acid in solution appears. 

 A Httle dilute NH4OH clears the turbidity. 



If we add acetic acid to luciferin solution until the precipitation 

 (probably a precipitate of mucin and nucleoprotein) is complete and 

 then dilute K4Fe(CN)6 solution, no further precipitate forms and 

 luciferin is found abundantly in the filtrate which gives no further 

 precipitate with K4Fe(CN)6 and acetic acid. These results are re- 

 corded in Table III. 



Luciferin is, therefore, very nearly completely precipitated by phos- 

 photungstic and tannic acids but not by picric acid. It is completely 

 precipitated unharmed by phosphotungstic acid + HCl, but not by 

 tannic acid + HCl or picric acid + HCl. It is not precipitated by 

 potassium ferrocyanide and acetic acid. Dubois^" finds Pholas 

 luciferin to be completely precipitated by picric acid. 



Heavy Metal Salts. 



Some of the heavy metal salts (Pb acetate, AgNOs, CUSO4) pre- 

 cipitate in sea water. As both crude luciferin and luciferase solu- 

 tions, although prepared with distilled water, contain small amounts 

 of the salts of sea water, a slight precipitate would be formed upon 

 addition of lead acetate. It is too small in amount to interfere with 

 the action of lead acetate as a precipitant, but it must be borne in 

 mind that some of the luciferin or luciferase might be adsorbed on 

 any precipitate formed, as this is especially likely to occur with inor- 

 ganic precipitates. Another difficulty encountered in precipitating 

 protein solutions with heavy metal salts is that in excess of heavy 

 metal salt some of the precipitate may redissolve. However, certain 

 definite results were obtained by precipitating crude luciferin and 

 luciferase with lead and mercury salts (the usual protein precipi- 

 tants) and these are described below although their interpretation 

 may be open to question. 



^^ Dubois, Ann. Soc. Linn. Lyons, 1913, Ix. 



