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Xanthine Oxidase (XO; EC 1.3.22) as well as Xanthine Dehydrogenase (XDH; EC 1.17.1.4) are two enzymes responsible for the last steps of purine metabolism, hydroxylation of a wide variety pyrimidine, pterin, and aldehyde. There are numerous publications evidencing not directly about regulating role of the hypoxanthine/xanthine existence and its catabolism in the row of the purine metabolic pathway. Activitie of XO were evaluated based on the method introduced by Litwack et all [1]. Protein quantity was calculated based on the Bradford methos. We have used Student t-test as well as ONE-WAY-ANOVA. We have chosen the best condition for evaluation of XO activity in the homogenate. The activity of XO in the rat brain in the presence of different substrates was the following in comparison with the control (1.2104±0.0000, p<0.05): for histidine 2.2190±0.4707, in the presence of allopurinol-1.6138±0.2690, for riboflavin 1.6138±0.1345 (with allopurinol - 1.4651±0.8773), for adenosine - 1.6138±0.2017 (with allopurinol - 1.2776±0.1345), for desoxyadenosine - 2.2997±0.5245, (with allopurinol - 1.2507±0.0672). We concluded, that regulation of Xanthineoxidoreductase by feedback mechanism might suppress the catabolism of purines and serves as a basis for the initiation of cells proliferative processes. [ABSTRACT FROM AUTHOR]

McManaman J.L. with colleages have purified Xanthine Oxidase (XO; EC 1.3.22) as well as Xanthine Dehydrogenase (XDH; EC 1.17.1.4) from the liver of the rats. During the experiments were used benzamidine-Sepharose based affinity chromatography as well as different types of electrophoreses. The results of isoelectric focusing are evidencing about the proteins with different values of pI: 6,13 and 6,23. Also, there was found out one more minor fraction with pI 6,07. However, it is necessarily to mention that all purified proteins were presented as an isoforms of XO. During further presentations authors do not mention about the possible existence of XD isoforms. We are presenting here the new method of XO purification with the utility of preparative electrophoresis, which guaranties visualization of all possible forms of XO. Activity of XO was evaluated based on the method introduced by Litwack et all. It was developed the new method based on the existing one, for the purification of XO from the liver of rats with the final utility of the preparative electrophoresis with further extraction of the proteins from the gel and evaluation of XO activity. For the calculation of the statistic we have used ONE-WAYANOVA (results were considered significant, when p<0.05) There were visualized by phoresis two bands possessing with XO activity. One of the bands had an approximate molecular weight equal to 300 kDa, the other one had approximately 40 kDa molecular weight. We have delineated also the activity of the XO in the pure fractions. Activity was detected in the first as well as 5th fractions (0.2317±0.0133-control, 0.3008±8.9803e-3-xanthine, 0.2155±0.0135-allopurinol in low concentration, 0.2326±0.0117-allopurinol in high concentration, p<0.01 for first fraction and 0.2004± 0.0544, 0.2298±0.0353, 0.2188 ±0.0393, 0.2249±0.0272 for 5th fraction). We have developed new method for XO purification and found out the XO activity in 2 different fractions with 10 times difference in molecular weight. [ABSTRACT FROM AUTHOR]