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Photoactivation is a technique used in biological research to specifically activate cellular players (proteins, nucleic acids, small molecules) by a flash of light in order to study processes in cells. The basic principle is to bring a photoactivatable agent (e.g. a small molecule modified with a light-responsive group, proteins tagged with an artificial photoreceptor protein) to cells, tissue or even living animals and specifically control the activity by illumination 〔Rana, A., & Dolmetsch, R. E. (2010). Using light to control signaling cascades in live neurons. Curr Opin Neurobiol, 20(5), 617–622. 〕 Light is a well-suited external trigger for these types of experiments since it is non-invasive and does not influence normal cellular processes (care has to be taken when using light in the ultra-violet part of the spectrum to avoid DNA damage. Furthermore, light offers high spatial and temporal control. Usually, the activation stimulus comes from a laser or a UV lamp and can be incorporated into the same microscope used for monitoring of the effect. All these advantages have led to the development of a wide variety of different photoactivatable probes. Even though the light-induced activation step is usually irreversible, reversible changes can be induced in a number of photoswitches, which will not be discussed in detail here. ==History== The first reported use of photoprotected analogues for biological studies was the synthesis and application of ‘caged’ ATP by Hoffman in 1978〔Kaplan, J. H., Forbush, B., & Hoffman, J. F. (1978). Rapid photolytic release of adenosine 5’-triphosphate from a protected analogue: utilization by the Na:K pump of human red blood cell ghosts. ''Biochemistry'', 17(10), 1929–35.〕 in his study of Na:K pumps. To this day, ATP is still the most commonly used caged compound. Hoffman was also the one to coin the term 'caged compound' for these type of modified molecules. This nomenclature continued to persist, even if it is not scientifically correct. It suggests the image of a molecule in a physical cage (like in a Fullerene), therefore scientists have tried to introduce the newer, more accurate term "photoactivatable probes". Both nomenclatures are currently in use. Small molecules are easier to modify by photocleavable groups, compared to larger constructs such as proteins. Major discoveries were made in the following years with caged neurotransmitters such as glutamate, which is used to map functional neuronal circuits in mammalian brain slices.〔Callaway, E. M., & Katz, L. C. (1993). Photoactivation with caged glutamate reveals functional circuitry in living brain slices. ''Proceedings of the National Academy of Sciences of the United States of America'', 90(16), 7661–5.〕 Photoactivatable proteins were serendipitously discovered much later (in 2002), by the observation that Kaede protein, when left on the bench exposed to sunlight, changed fluorescence to longer wavelength. (for an extensive review, visit:〔Chudakov, D., & Matz, M. (2010). Fluorescent proteins and their applications in imaging living cells and tissues. Physiological Reviews, 90(3), 1103–1163. PMID 20664080〕) 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「photoactivatable probes」の詳細全文を読む スポンサード リンク
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