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L-Photo-Leucine is a synthetic derivative of the L-Leucine amino acid that is used as its natural analog and is characterized for having photo-reactivity, which makes it suitable for observing and characterizing protein-protein interactions (PPI). When a protein containing this amino acid (A) is lightened with ultraviolet light while interacting with another protein (B), the complex formed from these two proteins (AB) remains attached and can be isolated for its study. Photo Leucine, as well as another photo-reactive amino acid derived from Methionine, Photo-Methionine, were first synthesized in 2005 by Monika Suchanek, Anna Radzikoska and Christoph Thiele from the Max Planck Institute of Molecular Cell Biology and Genetics with the objective of identifying protein to protein interaction throughout a simple western blot test that would provide high specificity. The resemblance of the photo-reactive amino acids to the natural ones allows the former ones to avoid the extensive control mechanisms that take place during the protein synthesis within the cell. ==Structure== As mentioned in the introduction, L-Photo-Leucine is a synthetic derivative of the L- Leucine amino acid. L-Photo-Leucine is characterized by the presence of a diazirine ring linked to the R radical of the original amino acid. This cyclopropene ring-shaped molecule is constituted of a carbon atom attached to two nitrogen atoms through a covalent single bond. These two nitrogen atoms are simultaneously connected to each other by a double covalent bond. The diazirine carbon is located in the position where theoretically the 2nd carbon atom of the R radical of L-Leucine would be, linked up with the 1st and 3rd carbon of this theoretical R radical. The diazirine ring confers to the Photo-Leucine its photoreactive property. When irradiated with UV light, it splits releasing nitrogen in gas form and leaving an unbound carbon atom (see Diazirine). In protein-protein interactions (PPI), this atom is attached to the complex formed by the two proteins susceptible of being under study. The rest of the amino acid has indeed the same structure as the original L-Leucine molecule, which includes, as every amino acid, an amino group and a carboxyl group bonded to an α-carbon, and a radical that is attached to this carbon atom. The R chain, contains, in this case, a diazirine ring and two extra carbon atoms connected each to the diazirine carbon as it has been previously mentioned.〔http://www.piercenet.com/product/photoreactive-amino-acids〕 It is also important to mention that only the L- isomer of the photo-leucine amino acid is synthetized. The reason for this lies in the fact that all human amino acids are found in the L form, and, therefore, if photo-leucine has to be introduced in human samples it is imperative for it to be in the L form. Currently, it's not fully know why all the human amino acids are found in the L- form, however, evidence suggests that L- amino acids are slightly more soluble than is the racemic mixture of D- and L- amino acids, which tends to form crystals. This small solubility difference could have been amplified over time to the point where the L- isomer became dominant in the solution. 〔Stryer L, Berg M.J, Tymoczko L. J. Bioquímica con aplicaciones clínicas. 7a ed. New York: Editorial Reverté. 2012〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「L-Photo-Leucine」の詳細全文を読む スポンサード リンク
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