Difference between revisions of "Part:BBa K1497000"
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Chalcone isomerase (CHI) catalyzes the intramolecular cyclization of bicyclic chalcones into tricyclic (S)flavanones. | Chalcone isomerase (CHI) catalyzes the intramolecular cyclization of bicyclic chalcones into tricyclic (S)flavanones. | ||
The pH dependence of flavanone formation indicates that both the non-enzymatic and enzymatic reactions first require the bulk phase ionization of the substrate 2-hydroxyl group and subsequently on the reactivity of the newly formed 2-oxyanion during C-ring formation. Solvent viscosity experiments demonstrate that at pH 7.5 the CHI-catalyzed cyclization reactions of 4,2,4,6 tetrahydroxychalcone, 4,2,4-trihydroxychalcone, and 2,4 dihydroxychalcone are 90% diffusion-controlled, where as cyclization of 4,2-dihydroxychalcone is limited by a chemical step that likely reflects the higher pKa of the 2-hydroxyl group. At pH 6.0, the reactions with 4,2,4,6 tetrahydroxychalcone and 4,2,4-trihydroxychalcone are 50% diffusion-limited, where as the reactions of both dihydroxychalcones are limited by chemical steps.<br/><br/> | The pH dependence of flavanone formation indicates that both the non-enzymatic and enzymatic reactions first require the bulk phase ionization of the substrate 2-hydroxyl group and subsequently on the reactivity of the newly formed 2-oxyanion during C-ring formation. Solvent viscosity experiments demonstrate that at pH 7.5 the CHI-catalyzed cyclization reactions of 4,2,4,6 tetrahydroxychalcone, 4,2,4-trihydroxychalcone, and 2,4 dihydroxychalcone are 90% diffusion-controlled, where as cyclization of 4,2-dihydroxychalcone is limited by a chemical step that likely reflects the higher pKa of the 2-hydroxyl group. At pH 6.0, the reactions with 4,2,4,6 tetrahydroxychalcone and 4,2,4-trihydroxychalcone are 50% diffusion-limited, where as the reactions of both dihydroxychalcones are limited by chemical steps.<br/><br/> | ||
Latest revision as of 20:30, 27 October 2020
Chalcone Isomerase (CHI) from Petunia
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The chalcone isomerse catalyzes the reaction from naringenin chalcone to naringenin. This enzyme is non-essential for flavanone pathways, because the reaction takes place independently from CHI in the cytosol. The enzyme independent reaction is catalyzed by an acidic compound. Without CHI the reaction is stereo unspecific. S-Naringenin is the active compound for the most enzymes in the biochemical pathways. To prevent gaining a racemic product and losing 50% yield, CHI is used, because only the enzyme is able to form 100 % S-Naringenin. |
Figure 1 Reaction of the CHI. A proton shift of naringenin chalcone builds naringenin. The CHI has a high E-value and produce only S-Naringenin. |
Added by BIT-China 2020
Chalcone isomerase (CHI) catalyzes the intramolecular cyclization of bicyclic chalcones into tricyclic (S)flavanones.
The pH dependence of flavanone formation indicates that both the non-enzymatic and enzymatic reactions first require the bulk phase ionization of the substrate 2-hydroxyl group and subsequently on the reactivity of the newly formed 2-oxyanion during C-ring formation. Solvent viscosity experiments demonstrate that at pH 7.5 the CHI-catalyzed cyclization reactions of 4,2,4,6 tetrahydroxychalcone, 4,2,4-trihydroxychalcone, and 2,4 dihydroxychalcone are 90% diffusion-controlled, where as cyclization of 4,2-dihydroxychalcone is limited by a chemical step that likely reflects the higher pKa of the 2-hydroxyl group. At pH 6.0, the reactions with 4,2,4,6 tetrahydroxychalcone and 4,2,4-trihydroxychalcone are 50% diffusion-limited, where as the reactions of both dihydroxychalcones are limited by chemical steps.
References:
Jez, J. M., & Noel, J. P. (2001). Reaction Mechanism of Chalcone Isomerase. Journal of Biological Chemistry, 277(2), 1361–1369. doi:10.1074/jbc.m109224200
Functional Parameters
The iGEM Team TU Darmstadt 2014 used the CHI and verified the function of the CHI in their naringenin operon (K1497007).
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21INCOMPATIBLE WITH RFC[21]Illegal XhoI site found at 284
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000INCOMPATIBLE WITH RFC[1000]Illegal BsaI.rc site found at 688