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BauernOpfer
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SleepyHollow02
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Untersuchte Arbeit:
Seite: 13, Zeilen: 1-10
Quelle: Nienhaus 2006
Seite(n): 4216, Zeilen: l.col.: 2 ff.
The schemes in figure 5, A and B, show the tightly coupled system of two protonatable groups between which protons can be shuttled. The small ratio between neutral and anionic population implies that only slight differences in free energies exist between the two conformations in the electronic ground state.

Tim 013a diss.png

Fig. 5. Schematic representation of the different protonation states of the AsGFP499 chromophore and its environment that are proposed to cause the spectral changes. (Nienhaus et al., 2006).

Upon photon absorption, this balance is disturbed. Phenols typically become more acidic upon electronic excitation (Tsien, 1998; Voityuk et al., 1998); and therefore, we expect efficient excited state proton transfer (ESPT) to Asp158, as is inferred from the observation that excitation in the A and B bands is equally efficient for fluorescence in the 499nm emission band for pH ˂ 8. Evidently, protonation of Asp158 is a key ingredient in the proton shuttling mechanism described above.

The schemes in Fig. 6, A and B, show the tightly coupled system of two protonatable groups between which protons can be shuttled. The small ratio between neutral and anionic population implies that only slight differences in free energies exist between the two conformations in the electronic ground state. Upon photon absorption, this balance is disturbed. Phenols typically become more acidic upon electronic excitation (9,52); and therefore, we expect efficient excited state proton transfer (ESPT) to Asp158, as is inferred from the observation that excitation in the A and B bands is equally efficient for fluorescence in the 499-nm emission band for pH < 8.

To further support the model presented in Fig. 6 by experimental evidence, we have produced the mutant Asp158Asn, which has its protonatable carboxyl residue replaced by a nonprotonatable carboxamide. Evidently, protonation of Asp158 is a key ingredient in the proton shuttling mechanism described above.

Tim 013a source.png

FIGURE 6 Schematic representation of the different protonation states of the asFP499 chromophore and its environment that are proposed to cause the spectral changes in Fig. 4.


9. Tsien, R. Y. 1998. The green fluorescent protein. Annu. Rev. Biochem. 67:509–544.

52. Voityuk, A. A., M. E. Michel-Beyerle, and N. Ro¨sch. 1998. Quantum chemical modeling of structure and absorption spectra of the chromophore in green fluorescent proteins. Chem. Phys. 231:13–25.

Anmerkungen

The source is given for the figure and its caption, but not for the remainder of the text.

Sichter
(SleepyHollow02), Hindemith

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