factors, such as time of heating, salt content, acidity, etc., so the luciferases of different animals coagulate at different temperatures depending on these conditions. Some of the more reliable observations on these critical temperatures are collected in [Table 14].
Table 14
Temperature Limits of Luminescence for Luminous Organism
| Organism | Author and date | Minimum | Optimum | Maximum |
|---|---|---|---|---|
| Pseudomonas javanica | Eijkman, 1892 | -20° | 25-33° | 45° |
| Bacterium phosphorescens | Lehmann, 1889 | -12° | ... | 39.5° |
| Bacterium phosphoreum | Molish, 1904, book | -5° | 16-18° | 28° |
| Light bacteria | Tarchanoff, 1902 | -7° | 15-25° | 37° |
| Light bacteria | Harvey, E. N., 1913 | -11.5 | 15-20° | 38° |
| Mycelium X | Molish, 1904 | ... | 15-25° | 36° |
| Lampyrids | Macaire, 1821 | -10 | 33° | 46-50° |
| Pyrophorus noctilucus | Dubois, 1886 | ... | 20-25° | 47° |
| Photuris pennsylvanica | Lund, 1911 | ... | ... | 50° |
| Luciola viticollis | Harvey, E. B., 1915 | <0° | ... | 42° |
| Cypridina hilgendorfii | Harvey, E. N., 1915 | <0° | ... | 52-54° |
| Cyclopina gracilis | Lund, 1911 | ... | ... | 50° |
| Phylirrhoë bucephalum | Panceri, 1872 | 44° | ... | 61° |
| Pyrosoma | Panceri, 1872 | <0° | ... | 60° |
| Mnemiopsis Leidyi | Peters, 1905 | 9° | 21° | 37° |
| Noctiluca miliaris | Quatrefages, 1850 | 1° | ... | 40° |
| Noctiluca miliaris | Harvey, E. B., 1917 | <0° | ... | 48° |
| Cavernularia haberi | Harvey, E. N., 1915 | <0° | ... | 52° |
| Watasenia scintillans | Shoji, R, 1919 | ... | 16-31° | 49° |
We are thus led to the conclusion that intensity of luminescence is dependent on the velocity of oxidation of luciferin and that with lowered reaction velocity the spectral composition of the light changes. The maximum emission shifts toward the yellow. I believe, however, that in Cypridina also, the luminescence intensity depends not only on reaction velocity but on the particular manner in which luciferin is oxidized. Cypridina luciferin will luminesce only in presence of Cypridina luciferase and no light can be obtained from Cypridina luciferin and a host of different oxidizers (with or without H2O2) such as are able to oxidize pyrogallol. Luciferin will also oxidize in the air spontaneously but no light is produced. It is easy to show that this spontaneous oxidation may be much more rapid than an oxidation with luciferase and yet light appears only in presence of the latter. If a concentrated solution of luciferin is kept near the boiling point it will be completely oxidized to oxyluciferin in four or five minutes. No light appears if air or even if pure oxygen is bubbled through it. The same solution kept at 20° with a small amount of luciferase will luminesce continuously and not be completely oxidized to oxyluciferin in a half hour. We can, however, cause the luciferin to oxidize as rapidly at 20° by adding concentrated luciferase as does the luciferin near the boiling point without luciferase. A bright light is produced in the former case, none in the latter case. The oxyluciferin
formed from spontaneous oxidation of luciferin appears to be the same as that formed with luciferase present. Both give luciferin again on reduction. Perhaps the reaction takes place in two stages, similar to those supposed to occur in other enzyme actions:
luciferin + luciferase = luciferinluciferase
luciferinluciferase + O (or minus H2) = oxyluciferin + luciferase.
We may then assume as a tentative hypothesis that luminescence only occurs during oxidation (addition of O or removal of H) of the luciferinluciferase compound.
We have just seen that the effect of cooling a Cypridina extract containing luciferin and luciferase and luminescing with a bluish light, is to reduce the intensity and change the shade toward the yellow. Velocity of oxidation must be lowered and with the same concentration of luciferase lowered velocity means more light of the longer wave-lengths. A very instructive experiment on color of the light can be carried out with animals having different colored lights and so closely related that their luciferins and luciferases will interact with each other. Such a case is presented by the American fireflies, Photinus and Photuris. Photinus emits an orange light, while Photuris emits a greenish yellow light. The difference in color is especially noticeable when the luminous organs of the two forms are ground up in separate mortars. As shown by Coblentz, the difference in color is real, the spectrum of Photinus extending farther into the red than that of Photuris (see [Fig. 8]). We can easily prepare luciferin and luciferase from the two fireflies and make the following mixtures: