Purification, properties, and application of a novel acid urease from Enterobacter sp.

It has been demonstrated that acid urease is capable of decomposing urea in fermented beverage and foods. As urea is a precursor of ethylcarbamate, a potential carcinogenic compound, measures must be taken to control the level of urea. We herein describe the purification and characterization of a novel acid urease from Enterobacter sp. R-SYB082 and its application to the removal of urea in Chinese rice wine. The enzyme was purified to electrophoretic homogeneity using ethanol precipitation, Superdex 200 and Mono Q with a fold purification of 21.1 and a recovery of 49%. The molecular weight of the enzyme was 430,000 Da by gel filtration and 72,000 Da by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that it was a hexamer. The activity of this purified enzyme was optimal at pH 4.5 and 35 degrees C. The temperature stability was under 55 degrees C, and the pH stability was 4.0~5.0. The enzyme exhibited an apparent K (m) of 19.5 micromol/l and a V (max) of 109 micromol urea/mg.min at 35 degrees C and pH 4.5. When incubating two different kinds of Chinese rice wine with the enzyme (0.08 U/ml) at 35 degrees C for 7 days, over 85% of urea was decomposed, and at 20 degrees C, above 78% was removed. The result showed that the enzyme is applicable to elimination of urea in Chinese rice wine.