Photocytes

A Photocyte is a cell that specializes in catalyzing enzymes to produce light (bioluminescence). Photocytes typically occur in select layers of epithelial tissue, functioning singly or in a group, or as part of a larger apparatus (a photophore).

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Light production is first triggered by nerve impulses which stimulate the photocyte to release the enzyme luciferase (Photinus Pyralis) into a "reaction chamber" of luciferin substrate. In some species the release occurs continually without the precursor impulse via osmotic diffusion. Molecular Oxygen is then actively gated through surrounding tracheal cells which otherwise limit the natural diffusion of Oxygen from blood vessels; the resulting reaction with the luciferase and luciferin produces light energy and a biproduct (usually carbon dioxide).

Researchers once postulated that ATP was source of reaction energy for photocytes, but since ATP only produces a fraction the energy of the luciferase reaction, any resulting light wave-energy would be too small for detection by a human eye. The wavelengths produced by most photocytes fall close to 490 nm; although light as energetic as 250 nm is reportedly possible.

The variations of color seen in different photocytes are usually the result of color filters that alter the wavelength of the light prior to exiting the endoderm. The range of colors vary between bioluminescent species.

Interestingly, the exact combinations of luciferase and luciferin types found among photocytes are specific to the species to which it belongs. This would seem to be the result of consistent evolutionary divergence.