PURIFICATION AND CHARACTERIZATION OF D-TAGATOSE 3-EPIMERASE FROM PSEUDOMONAS SP, ST-24

A new enzyme, D-tagatose 3-epimerase, was found in Pseudomonas sp. ST-24 during the course of studies on D-sorbose fermentation. This new enzyme catalyzes epimerization of keto-sugars, for example between D-tagatose and D-sorbose, and between D-fructose and D-psicose. It was shown that this enzyme epimerizes the configuration at the C-3 position of these substrates. This epimerase didn't act on D-fructose 6-phosphate and D-ribulose 5-phosphate. The enzyme has been purified from cells grown on a medium containing 1% D-glucose and 0.05% D-tagatose, and it appeared homogeneous on electrophoresis. The enzyme has a molecular weight of about 68,000 by gel filtration and consists of two subunits identical in molecular weight (about 33,000 by SDS-PAGE). The maximum activity at 30 degrees C was obtained at pH 7-9, and the enzyme was stable from pH 7-11. The optimum temperature was around 60 degrees C, and it was stable up to 60 degrees C for 10 min.