100 Papers from the Department of Marine Biology. 
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 inorganic precipitates. 
Another difficulty encountered in precipitating protein solutions with 
heavy metal salts is that in excess of heavy metal salt some of the pre- 
cipitate may redissolve. However, certain definite results were obtained 
by precipitating crude luciferin and luciferase with lead and mercury 
salts (the usual protein precipitants),and these are described below, 
although their interpretation may be open to question. 
Neutral lead-acetate solution was added to crude luciferase solution, 
drop by drop, until no further precipitate formed. The filtrate was 
clear and gave no further precipitate on adding more lead acetate. It 
gave a good light with excess of luciferin. The precipitate suspended 
in water does not dissolve, but upon addition of luciferin gives a bright 
light. 
Basic lead acetate added drop by drop gives a bulky precipitate, 
leaving a clear filtrate which gives no further precipitate on addition 
of more basic lead acetate. This filtrate gives no light with excess 
luciferin, but the precipitate washed once with water on the filter gives 
a bright light. 
Saturated HgCl, solution was added drop by drop to luciferase solu- 
tion until no further precipitate occurs. The filtrate is perfectly clear 
and gives a bright light with luciferin, although it gives no further 
precipitate with HgCl,. The precipitate washed on the filter for 20 
hours in running water is suspended in water. It does not completely 
dissolve, but on addition of luciferin gives a fair light. 
Luciferase, therefore, is completely precipitated by basic lead acetate, 
nearly completely precipitated by neutral lead acetate, but not pre- 
cipitated by mercuric chloride. 
If a saturated solution of HgCl, is added drop by drop to luciferin 
solution a precipitate forms. If this is filtered off, washed with dilute 
HgCl., and suspended in water, it does not completely dissolve, but gives 
a good light if an excess of luciferase is added. The opalescent filtrate 
which gives no further precipitate with HgCl, gave a fair light on adding 
an excess of luciferase. Mercuric chloride and acetic acid almost 
completely precipitate luciferin from solution. 
Neutral lead-acetate solution added to luciferin gives a heavy precip- 
itate. The solution filters cloudy at first, even though no further 
precipitate forms on adding lead acetate, but soon filters clear. This 
clear filtrate containing some Pb gives a bright light on addition of 
excess of luciferase. The precipitate was washed several times on the 
filter and by decantation with dilute Pb acetate, and suspended in 
water. It does not completely dissolve, but gives a good light with 
luciferase. Lead acetate and acetic acid give no good precipitate with 
crude luciferin. 
