Purification and characterization of flavonol 3-glucosidase, and its activity during ripening in tartary buckwheat seeds

Abstract

To obtain basic information about rutin metabolism in buckwheat seeds, flavonol 3-glucosidase (f3g) was purified from tartary buckwheat ( Fagopyrum tataricum) seeds. The f3g consisted of two isozymes, and their characteristics were very similar to the rutin-degrading enzyme (RDE) reported in [Phytochemistry 37 (1994) 133], although the molecular weight and kinetic constants were quite different. In addition, rutin and isoquercitrin concentrations and corresponding f3g activities were measured during the ripening of tartary and common buckwheat seeds. Rutin and isoquercitrin increased during ripening, and the rutin concentration remained high in the fully ripe seeds. The rutin 3-glucosidase activity and isoquercitrin 3-glucosidase activity also increased during ripening and remained high with a slight reduction in fully ripe seeds. In such seeds, the major part of the rutin was found in the embryo, and almost all the f3g activity was detected in the testa. These results support the hypothesis that the f3g activity is not the major limiting factor of the rutin concentration in fully ripe seeds.