90 Papers from the Department of Marine Biology. 
precipitated Fe(OH) or As.S3, infusorial earth, talc, or kaolin. If one 
mixes colloidal Fe(OH); with dilute luciferase or dilute luciferin and 
then precipitates the Fe(OH) ; with a little Na .SO,, the luciferase or 
luciferin will also be completely precipitated mixed with the Fe(OH)3. 
If luciferin or luciferase are more concentrated there will be only par- 
tial precipitation with the Fe(OH)3. 
Most of the precipitants for luciferin and luciferase belong to the 
group of protein precipitants, but it must always be borne in mind that 
both of these substances may merely come down together with the 
proteins associated with them. It is, therefore, very difficult to say 
definitely from precipitation reactions whether luciferin and luciferase 
are proteins or merely adsorbed by protein precipitates. In many 
cases one can control this possibility by testing directly their adsorp- 
tion on protein precipitates, and such experiments are referred to in the 
subsequent sections of this paper. Dubois! has come to the conclu- 
sion that Pholas luciferin and luciferase are proteins. He has been, 
however, by no means careful to give detailed description, or a critical 
analysis of his experiments,and he apparently has not considered the 
possibility of adsorption. Both Cypridina luciferin and luciferase 
certainly possess many properties in common with the proteins, but it 
will be more fitting to discuss their protein nature after describing in 
detail their chemical characteristics. 
The following subjects will be considered: (1) Action of enzymes. 
(2) Salting out. (8) Alcohol and acetone. (4) Solubility in organic 
solvents. (5) Alkaloidal reagents. (6) Heavy metal salts. (7) Acids 
and alkalies. (8) Adsorbents. 
ACTION OF ENZYMES. 
Table 1 gives the results of enzyme experiments. A solution of 
crude luciferase (or crude luciferin) was mixed with the enzyme prepa- 
ration and kept at 38° C. in an incubator for from 18 hours to 4 days. 
Controls were always employed, using previously boiled enzyme solu- 
tion. Experiments were also made to determine if the particular 
enzyme preparation was active on its substrate and no experiments 
were considered in which this was found not to be the case. After the 
enzyme solution had acted for the proper length of time on the photo- 
genic substances their light-giving power was tested by adding an 
equal amount of luciferin (orluciferase) to both controland active tubes, 
and comparing the brightness of the light resulting from the active 
tube with that of the control. In order to prevent oxidation the digests 
of luciferin were carried out in long test-tubes, full of solution, which 
were either corked or covered with a thick layer of vaseline. This pro- 
cedure is not necessary in the case of luciferase. 
1 Dubois regards Pholas luciferin as a natural albumin and luciferase as an oxidizing enzyme 
made up of iron associated with a protein. ‘‘La Vie et la Lumiére;’’ Paris, 1914. 
