綠色熒光蛋白（GFP）是一種蛋白質，存在于北太平洋發現的水母，維多利亞水母（Aequorea victoria）中。熒光是一種現象，某些物質會吸收電磁輻射（例如光）中的能量，并以不同的波長（通常更長）發射能量。GFP產生的綠色發光是由于它吸收了相對較高能量的藍色和紫外線發出波長較長，能量較少的綠光。因此，當暴露于不可見的紫外線下時，它會發出綠色光。GFP與生物學家特別感興趣，因為與大多數其他熒光蛋白不同，GFP自身發出熒光，而無需與其他分子發生任何相互作用。由于它是一種完全由氨基酸組成的蛋白質，因此這意味著可以對生物進行基因工程改造以生產它，從而在生物學的各個領域產生了廣泛的應用。

生物發光發生在許多海洋生物中。對于維多利亞水母，化學發光物質稱為水母發光蛋白，當它與鈣離子結合時會發出藍光。然后，該光被綠色熒光蛋白吸收，產生綠色發光。已經發現許多其他海洋生物也包含這些物質，但不清楚為什么它們進化產生這種光輝或將顏色從藍色變為綠色。根據實驗證據表明，發光的GFP可以釋放電子，一個建議是GFP可以起到光活化電子供體的作用，類似于綠色植物中的葉綠素。

綠色熒光蛋白具有復雜的結構。熒光部分-稱為熒光發色團-由三個氨基酸組成，酪氨酸，甘氨酸和絲氨酸或蘇氨酸以環狀連接。它包含在保護發色團免于與其他分子接觸的圓柱形結構中，這對熒光至關重要，因為與水分子接觸會消散用于產生綠色光的能量。

事實證明，GFP在遺傳學，發育生物學，微生物學和神經病學等領域極為有用。它可用于標記生物體內的特定蛋白質，以查看它們在何時何地表達；生物體DNA的一部分可以對編碼目的蛋白的蛋白進行改造，使其也能合成GFP，從而允許使用紫外線在活細胞內跟蹤蛋白。也可以通過這種方式標記病毒，從而可以監測活生物體中的感染。還可以對綠色熒光蛋白進行修飾，使其發出其他幾種顏色的熒光，從而開辟了新的可能性。其中之一是創建具有在神經元中表達的熒光蛋白的各種組合的轉基因小鼠，從而可以詳細研究大腦中的神經通路。

在生物學之外還發現了其他應用。一個有爭議的發展是熒光寵物的工程。已經產生了產生綠色熒光蛋白的基因工程動物，其中包括魚，大鼠，豬和兔子。

Green fluorescent protein (GFP) is protein that occurs in a species of jellyfish, Aequorea victoria, which is found in the North Pacific. Fluorescence is a phenomenon whereby certain substances absorb energy from electromagnetic radiation, such as light, and emit the energy at a different, normally longer, wavelength. The green glow produced by GFP results from it absorbing relatively high-energy blue and ultraviolet light and emitting it as green light, which has a longer wavelength and less energy; it will therefore glow green when exposed to invisible ultraviolet light. GFP is of particular interest to biologists as, unlike most other fluorescent proteins, it fluoresces by itself without the requirement for any interaction with other molecules. Since it is a protein made up entirely of amino acids, this means that organisms can be genetically engineered to produce it, giving rise to a wide range of applications in various fields of biology.

Bioluminescence occurs in many marine organisms. In the case of Aequorea victoria, a chemiluminescent substance called aequorin emits blue light when it combines with calcium ions. This light is then absorbed by the green fluorescent protein to produce a green glow. A number of other marine organisms have been found to contain these substances, but it is not clear why they have evolved to produce this glow or to change the color from blue to green. One suggestion, based on experimental evidence that glowing GFP can release electrons, is that GFP could act as a light-activated electron donor, in a similar way to chlorophyll in green plants.

The green fluorescent protein has a complex structure. The fluorescent part — known as a fluorescent chromophore — consists of three amino acids, tyrosine, glycine and either serine or threonine, joined in a ring shape. This is contained within a cylindrical structure that protects the chromophore from contact with other molecules, a feature that is crucial to the fluorescence, as contact with water molecules would otherwise dissipate the energy used to produce the green glow.

GFP has proved to be extremely useful in fields such as genetics, developmental biology, microbiology and neurology. It can be used for tagging specific proteins within an organism in order to see where and when they are expressed; the part of the organism’s DNA that codes for the protein of interest can be engineered to also synthesize GFP, thus allowing tracking of the protein within living cells using ultraviolet light. Viruses can also be tagged in this way, allowing infections in living organisms to be monitored. Green fluorescent protein can also be modified to fluoresce in several other colors, opening up new possibilities. One of these has been the creation of transgenic mice with varying combinations of fluorescent proteins expressed in neurons, which allow neural pathways in the brain to be studied in detail.

Other applications have been found outside biology. One controversial development is the engineering of fluorescent pets. Genetically engineered animals that produce green fluorescent protein have been created, and include fish, rats, pigs and a rabbit.