An investigation of flavonol glucosyltransferase activity in grapevine tissues

Abstract

Flavonols are important components of the berry-derived non-pigmented phenolic compounds found in wines. In common with many plant compounds, they are conjugated to sugar molecules by enzymes called glycosyltransferases. The enzymes responsible for this in grapevine tissues have not been isolated. The research aimed to achieve a preliminary characterisation of flavonol glucosylating activity in grapevine tissues, and to suggest approaches for a future purification of the enzyme.

Summary

While flavonols are important berry-derived phenolic compounds found in wines, the enzymes (called glycosyltransferases) which conjugate these to sugars have not been well understood. This research aimed to achieve preliminary characterisation of flavonol-glucosylating activity in tissues.

The study involved extraction of total soluble proteins using buffer solutions to minimise interactions between protein components of tissue and its high content of polyphenolic compounds, and application of assays for the formation of flavonol glucosydes. Qualitative and quantitative glucosylation assays were developed and the formation of glucosides of a range of flavonoid compounds was studied. Enrichment of protein fractions for glucosyltransferase activity was examined by continuous gradient ion exchange chromatography. Pseudo-affinity dye chromatography, used in the purification of a number of glucosyltransferases from other plants, was tested for its usefulness in isolating the flavonol glucosylating activity.

In addition to the interesting observation that specific flavonoids may be glucosylated by specific enzyme activities, the work has helped refine techniques for understanding enzyme activity.