User:Matt Whelihan: Difference between revisions
From Proteopedia
Jump to navigationJump to search
No edit summary |
No edit summary |
||
| Line 12: | Line 12: | ||
These seven highly conserved amino acids identify the <scene name='User:Matt_Whelihan/Active_site_residues/1'>active site</scene> which is located in the large hydrophobic cleft between the two adjacent N and C-terminal domains. | These seven highly conserved amino acids identify the <scene name='User:Matt_Whelihan/Active_site_residues/1'>active site</scene> which is located in the large hydrophobic cleft between the two adjacent N and C-terminal domains. | ||
Firefly luciferases catalyze the formation of the <scene name='User:Matt_Whelihan/Complete_active_site/1'>luciferin-adenylate intermediate</scene>. A proton is then abstracted in a steriospecific manner from the C-4 carbon, presumably by an <font color='gold'>enzyme base</font> believed to be <scene name='User:Matt_Whelihan/Complete_active_site/3'>Thr343</scene>. A conformational change then occurs which allows molecular oxygen addition to the newly formed anion. As the highly reactive dioxetanone intermediate decays to the ground state, it releases a photon of light<ref>PMID:7000855</ref><ref>PMID:4813372</ref>. | Firefly luciferases catalyze the formation of the <scene name='User:Matt_Whelihan/Complete_active_site/1'>luciferin-adenylate intermediate</scene>. A proton is then abstracted in a steriospecific manner from the C-4 carbon, presumably by an <font color='gold'>enzyme base</font> believed to be <scene name='User:Matt_Whelihan/Complete_active_site/3'>Thr343</scene>. A conformational change then occurs which allows molecular oxygen addition to the newly formed anion. As the highly reactive dioxetanone intermediate decays to the ground state, it releases a photon of light<ref>PMID:7000855</ref><ref>PMID:4813372</ref>. | ||
[[Image: | [[Image:redgreen.jpg]] | ||
One of the most intriguing parts of this mechanism is about how various firefly species are able to emit different types of light with the same exact reaction. It had been hypothesized for 20 years that the enol form was responsible for the typical yellow green spectra at neutral pH by an enzyme assisted tautomerization. The keto form of the intermediate which is seen at low pH gave rise to the red spectra, presumably due to a less stable charge transfer leading to a less efficient conversion into the lower energy red Various mutational studies by Branchini et al. showed that seven residues <scene name='User:Matt_Whelihan/Red_shift/1'>His245, Phe247, Arg218, Ala348, Gly341, Asp422 and Thr343</scene> were responsible for controlling the resonance-based charge delocalization of the anionic keto form of oxiluciferin <ref>PMID:15182171</ref>. This control of resonance charge on the molecule is paramount in the enzymes ability to catalyze the yellow green emission of light following oxidation of the substrate. Various species have evolved with subtle variations in their active site structures which in turn yields a large spectral shift as the keto form of the oxyluciferin is favored. | One of the most intriguing parts of this mechanism is about how various firefly species are able to emit different types of light with the same exact reaction. It had been hypothesized for 20 years that the enol form was responsible for the typical yellow green spectra at neutral pH by an enzyme assisted tautomerization. The keto form of the intermediate which is seen at low pH gave rise to the red spectra, presumably due to a less stable charge transfer leading to a less efficient conversion into the lower energy red Various mutational studies by Branchini et al. showed that seven residues <scene name='User:Matt_Whelihan/Red_shift/1'>His245, Phe247, Arg218, Ala348, Gly341, Asp422 and Thr343</scene> were responsible for controlling the resonance-based charge delocalization of the anionic keto form of oxiluciferin <ref>PMID:15182171</ref>. This control of resonance charge on the molecule is paramount in the enzymes ability to catalyze the yellow green emission of light following oxidation of the substrate. Various species have evolved with subtle variations in their active site structures which in turn yields a large spectral shift as the keto form of the oxyluciferin is favored. | ||
---- | ---- | ||
