Measurement of the activity of polyuronic acid C-5 epimerases

A relatively simple assay procedure for measuring the reactions catalyzed by polyuronic acid C-5 epimerases has been developed. Action of C-5 epimerases inverts the C-6 carboxyl group of polyuronic acids converting beta-linked residues into alpha-linked residues or vice versa. The assay takes advantage of the greater susceptibility of the acid hydrolysis of alpha-glycosidic linkages than beta-glycosidic linkages. The method involves the partial acid hydrolysis of the polyuronic acid before and after reaction with the C-5 epimerase. The greater or lesser amounts of uronic acid released (solubilized) before and after reaction of the C-5 epimerase are a measure of the amount of alpha- or beta-glycosidic linkages that are formed and a measure of the amount of catalysis by the enzyme.