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. 2015 Apr 14;20(4):6640-53.
doi: 10.3390/molecules20046640.

A Three-Enzyme-System to Degrade Curcumin to Natural Vanillin

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Free PMC article

A Three-Enzyme-System to Degrade Curcumin to Natural Vanillin

Vida Esparan et al. Molecules. .
Free PMC article

Abstract

The symmetrical structure of curcumin includes two 4-hydroxy-3-methoxyphenyl substructures. Laccase catalyzed formation of a phenol radical, radical migration and oxygen insertion at the benzylic positions can result in the formation of vanillin. As vanillin itself is a preferred phenolic substrate of laccases, the formation of vanillin oligomers and polymers is inevitable, once vanillin becomes liberated. To decelerate the oligomerization, one of the phenolic hydroxyl groups was protected via acetylation. Monoacetyl curcumin with an approximate molar yield of 49% was the major acetylation product, when a lipase from Candida antarctica (CAL) was used. In the second step, monoacetyl curcumin was incubated with purified laccases of various basidiomycete fungi in a biphasic system (diethyl ether/aqueous buffer). A laccase from Funalia trogii (LccFtr) resulted in a high conversion (46% molar yield of curcumin monoacetate) to vanillin acetate. The non-protected vanillin moiety reacted to a mixture of higher molecular products. In the third step, the protecting group was removed from vanillin acetate using a feruloyl esterase from Pleurotus eryngii (PeFaeA) (68% molar yield). Alignment of the amino acid sequences indicated that high potential laccases performed better in this mediator and cofactor-free reaction.

Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Hypothetical pathway of laccase-catalyzed biotransformation of curcumin. (1) Curcumin; (2) O-centered curcumin radical; (3) C-centered curcumin radical; (4,5) C-centered radicals in the alkenyl chain of curcumin; (6,7) intermediate 1,2-endoperoxides of the curcumin radical; (8) Vanillin; (9) Ferulic acid.
Figure 2
Figure 2
Partial amino acid alignment of LccFtr (Funalia trogii), LccMgi (Meripilus giganteus) and LccAbi (Agaricus bisporus). Bold letters show three out of four invariable T1 copper ligands, bold and italic letters the variable axial ligand and letters highlighted in grey a characteristic tripeptide of the binding site of T1 copper indicative of the redox potential of the respective laccases.
Figure 3
Figure 3
Three-step enzymatic bioconversion of curcumin to natural vanillin.

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