C42: Metabolism of Condensed Tannins by Manganese Peroxidase

Tannin is a chemically stable phenolic compound found in plant leaves, fruits, and roots. It enters the soil from plant detritus, but what happens after it enters the soil is unknown. It has biological importance due to its action as an antioxidant and its ability to precipitate proteins. This unique ability to interact with proteins, however, may inactivate some enzymes, so the breakdown of this compound in soil is unclear. Manganese peroxidase is an enzyme from white-rot fungi that catalyzes the oxidation of Mn(II) to Mn(III), which can then diffuse away from the enzyme to oxidize other larger compounds. It has been known to oxidize lignin, another plant compound related to tannin. A method has been developed to confirm the breakdown of catechin and epicatechin monomers, as well as a dimer, by manganese peroxidase. This method combines a substrate, such as catechin, with manganese (II) sulfate, hydrogen peroxide, oxalate buffer, and manganese peroxidase and allows oxidation of the components to occur. The products are then visualized by TLC and analyzed using ImageJ. In our study, we optimize this method to visualize the greatest degree of disappearance of the substrates, and then apply that method to other polymers of tannin. The breakdown of sorghum tannin and cocoa tannin, a slightly smaller polymer, were not successfully seen using TLC, so we employ the reaction with smaller polymers next, such as catechin trimer. We found that the trimer reacted at a much faster rate than the dimer compounds, suggesting a possible mechanism for degradation at the terminal units of the polymers. Future research exploring the identity of the products from these reactions may provide valuable information as to how tannins are broken down in soil to impact nutrient recycling and possible ramifications for human and animal digestion of dietary tannins.

Author(s): Jenna McLain, Biology and Nutrition Major

Advisor(s): Ann Hagerman, Department of Chemistry and Biochemistry
Meiling Fu, Department of Chemistry and Biochemistry