Part:BBa_K1497000

Chalcone Isomerase (CHI) from Petunia

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. 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.

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.

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

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal XhoI site found at 284
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 688