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In order to fast and economically purify MTGase from Streptoverticillium ladakanum, a stepwise elution method was developed and compared with linear gradient elution method. MTGase was purified to electrophoretical homogeneity by using CM Sepharose CL-6B and Blue Sepharose Fast Flow chromatographies by linear gradient or stepwise methods. The recovery of MTGase by linear gradient and stepwise methods were 68.4% and 81.0%, respectively. The optimal temperature and pH were 40 °C and 5.5, respectively. It was stable at pH 5.0 to 7.0 and had a rate constant (K D ) of 6.21 ∞ 10 -5 min -1 for thermal inactivation at 45 °C.After 4 d incubation of S. ladakanum, the culture fluid was filtered through 0.22 m filter paper. The production of MTGase

Using a fractionation technique, four phytochemicals were isolated from Rhodiola crenulata extracts. These compounds were identified as 4'-hydroxyacetophenone (4-HAP), epicatechin-(4β,8)-epicatechin gallate (B2-3'-O-gallate), salidroside, and p-tyrosol using mass spectrometry and nuclear magnetic resonance spectroscopy. The inhibition of xanthine oxidase (XO) activity by these purified compounds was then evaluated and compared to that of a known XO inhibitor (allopurinol; IC50 = 12.21 ± 0.27 μM). Both 4-HAP and B2-3'-O-gallate showed an XO inhibitory effect, for which the half maximal inhibitory concentration (IC50) values were 15.62 ± 1.19 and 24.24 ± 1.80 μM, respectively. However, salidroside and p-tyrosol did not show significant inhibitory effects on XO at 30 μM. Furthermore, an inhibition kinetics study indicated that 4-HAP and B2-3'-O-gallate are mixed competitive inhibitors. The inhibition constants (Ki) of 4-HAP and B2-3'-O-gallate were 8.41 ± 1.03 and 6.16 ± 1.56 μM, respectively. These results suggest that 4-HAP and B2-3'-O-gallate are potent XO inhibitors.