Finally, we have the fluorescent substance of Pyrophorus and fireflies, which Dubois first called pyrophorin,
but later, adopting McDermott's terminology, speaks of as luciferesceine. This Dubois regards as a substance intensifying the light and modifying its color by changing invisible into visible rays. As we have seen, this theory, while attractive, will not stand the test of critical examination.
Phipson's noctilucin, while the first name for the photogen of luminous animals, is too vague a substance, chemically, to warrant a retention of the term. Of the names, luciferin, luciferase, preluciferin or proluciferin, co-luciferase, photogenin, photophelein, oxyluciferin, luciferesceine, I believe that only proluciferin, luciferin, oxyluciferin, luciferase and photophelein stand for substances which are really significant for the theory of light production. Luciferin is the heat resistant, dialyzable substance which takes up oxygen and oxidizes with light production in the presence of the heat sensitive, non-dialyzing, enzyme-like luciferase. The luciferin must come from some precursor, proluciferin, but I have been unable to demonstrate the existence of this body in Cypridina and know nothing definite of its properties. The luciferin oxidizes to oxyluciferin which has the same chemical properties as the luciferin itself and may be reduced to luciferin again by reducing substances in luminous and other animals or by inorganic reducing agents. Photophelein is a name for substances in various animal or plant extracts which are capable of liberating luciferin from some bound condition in solutions containing luciferase. Under this term are included a number of unknown, probably quite different substances, some of which are thermostable and others thermolabile.
We have seen that Bioluminescence is an oxylumines
cence, that the light is probably due to the oxidation of a compound, luciferin, in presence of air and water and that the oxidation is accelerated by an enzyme-like substance, luciferase. We also saw in [Chapter 2] that light production is of fairly common occurrence during the oxidation of many organic compounds, provided the oxidation is carried out in the proper way. Many of these organic compounds must be oxidized by relatively strong alkali or such strong oxidizing agents as would have a very deleterious action on living cells. In 1913, Ville and Derrien, in a short note to the French Academy, "Catalyse Biochemique d'une Oxydation Luminescente," show that lophin could be oxidized by vertebrate blood in the presence of H2O2. In the same year Dubois (1913) found that esculin, the glucoside from horse chestnut bark, would also oxidize and luminesce in presence of blood and H2O2. In these cases the hæmoglobin of the blood acts as a catalyst, transferring oxygen from the H2O2 to esculin or lophin and is to be compared to luciferase, except that luciferase does not require the presence of H2O2.
As the hæmoglobin does not lose this power on boiling, whereas luciferase does, the analogy is far from perfect. Many oxygen carriers are known, however, which may be destroyed on boiling their solutions, namely, the peroxidases of plant juices. Esculin will not luminesce with peroxidase and H2O2, but pyrogallol or gallic acid will. If one mixes a test tube containing pyrogallol solution + H2O2 with potato or turnip juice or almost any plant extract, a yellowish luminescence appears. The plant extract loses the power to cause such luminescence on boiling and the peroxidase will not dialyze. It is, of course, comparable to luciferase and acts on the thermostable, dialyz
able pyrogallol-H2O2 mixture, which is comparable to luciferin. Curiously enough, although many hydroxyphenol and amino-phenol compounds can be oxidized by peroxidase and H2O2, only pyrogallol and gallic acid will oxidize with light production. Many other oxidizers can take the place of the peroxidase. A list of these is given on [page 151]. No other peroxide can take the place of H2O2 with peroxidases as oxidizers, but a few can replace H2O2 with other oxidizers. This is brought out in [Table 7].
Table 7
Peroxides Giving Light with Pyrogallol and Oxidizers
| Oxidizer. (Equal parts added to a mixture of M/100 pyrogallol and the peroxide) | H2O2 3 per cent. | Benzoyl hydrogen peroxide (insoluble powder) | Ozonized turpentine (one drop) | Na2O2 (powder) | BaO2 (powder) | MnO2 (insoluble powder) | PbO2 (insoluble powder) | K persulfate M/10 | Na perborate M/20 | K perchlorate M/10 | Quinone (insoluble crystals) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Turnip juice | + | - | - | - | - | - | - | - | - | ||
| 1 percent blood extract | + | - | - | Faint flash | - | - | - | - | - | - | - |
| M 20 K4Fe(CN)6 | + | - | - | - | - | - | - | - | - | - | - |
| M 100 KMnO4 | + | - | - | - | - | - | - | Faint flash | Fair flash | - | - |
| M 10 FeCl3 | + | - | - | ||||||||
| M 100 CrO3 | + | - | - | ||||||||
| Na hypobromite | + | - | - | Faint flash | Faint flash | - | - | Fair flash | Fair flash | - | |
| Ca hypochlorite | + | - | - | - | - | - | - | Faint | Fair flash | - | - |
| MnO2 | + | ||||||||||
| Mn(OH)3 sol in peptone | + | - | - | ||||||||
| Colloidal Ag | + |
Our knowledge of the existence of such analogous, purely organic chemical oxidations, which proceed with light production, greatly strengthens Dubois' theory that