Photocytes
Encyclopedia
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
).
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 by-product (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, thanks to the other parts of the photophore
. 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.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
that specializes in catalyzing enzymes to produce light (bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
). Photocytes typically occur in select layers of epithelial tissue, functioning singly or in a group, or as part of a larger apparatus (a photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
).
Light production is first triggered by nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
impulses which stimulate the photocyte to release the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
luciferase
Luciferase
Luciferase is a generic term for the class of oxidative enzymes used in bioluminescence and is distinct from a photoprotein. One famous example is the firefly luciferase from the firefly Photinus pyralis. "Firefly luciferase" as a laboratory reagent usually refers to P...
(Photinus Pyralis) into a "reaction chamber" of luciferin
Luciferin
Luciferins are a class of light-emitting biological pigments found in organisms that cause bioluminescence...
substrate. In some species the release occurs continually without the precursor impulse via osmotic diffusion
Osmosis
Osmosis is the movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration, aiming to equalize the solute concentrations on the two sides...
. Molecular Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
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 by-product (usually carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
).
Researchers once postulated that ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
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
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of the light prior to exiting the endoderm, thanks to the other parts of the photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
. The range of colors vary between bioluminescent species.
Interestingly, the exact combinations of luciferase
Luciferase
Luciferase is a generic term for the class of oxidative enzymes used in bioluminescence and is distinct from a photoprotein. One famous example is the firefly luciferase from the firefly Photinus pyralis. "Firefly luciferase" as a laboratory reagent usually refers to P...
and luciferin
Luciferin
Luciferins are a class of light-emitting biological pigments found in organisms that cause bioluminescence...
types found among photocytes are specific to the species to which it belongs. This would seem to be the result of consistent evolutionary divergence.