A spectrophotometric method for the determination of three forms of xanthine oxidoreductase, namely dehydrogenase (D), dehydrogenase-oxidase (D/0) and oxidase (0)

Data processing using nonparametric statistics was performed using a 'direct linear plot' algorithm of ECB. ECB (Eisenthal and Cornish-Bowden) is a computer program designed to calculate the Km and V parameters in enzyme kinetics. It is also suitable for estimation of EC50 (ligand or drug concentration for 50% effect) in pharmacological studies.

The effects of 2-iodosobenzoic acid, 4-chloromercuribenzoate, 5,5'-dithiobis-(2-nitrobenzoic acid) and tetraethylthioperoxydicarbonic diamide (disulphiram) on the NAD+-dependent activity of xanthine oxidoreductase from rat liver were investigated. Only disulphiram converted the NAD+-dependent activity into the O2-dependent activity quantitatively, without changing the xanthine hydroxylation rate. The modification process was a first-order reaction with respect to time (min) and disulphiram concentration (microM). The kinetic data showed that modification of single thiol group is sufficient for loss of the enzymic activity towards NAD+ as electron acceptor. The complete protection afforded by NAD+ against the action of disulphiram suggests that the essential thiol group may be involved in binding of NAD+ to the xanthine oxidoreductase molecule.

Abstract. The Astro Izery project is carried by several institutions from Poland and Czech Republic. Its aim is to educate and inform tourists, who visit the Izery Mountains, about astronomy and light pollution. The project consists of two activities: permanent (sundials, planetary path etc.) and periodic (meetings, workshops). After five years the project is in good health and will gain more elements in next years.

The enzyme xanthine: acceptor oxidoreductase found in rat heart equilibrates between three forms differing in electron acceptor specificity. Form D transfers electrons exclusively to NAD+ and accounts for 85% of total oxidoreductase activity. Form O transfers electrons to molecular oxygen and accounts for 8%. The D/O form prefers NAD+, but without NAD+ transfers electrons to oxygen. Interconversion from D to O and O to D forms is catalyzed by sulfhydryl group-modifying reagents: Cd2+, Cu2+, disulfiram, and heating with dithiothreitol. This suggests that sulfhydryl groups participate in the first stage of enzyme conversion. The NADH/NAD+ concentration ratio may regulate the dehydrogenase activity of xanthine:acceptor oxidoreductase (NAD+-dependent activity of D and D/O forms). Accumulating NADH inhibits hypoxanthine hydroxylation. The amount of form O increases during cardiac ischemia, facilitating superoxide radical-ion generation. Also, NADH/NAD+ does not regulate form O, promoting adenylate nucleotide pool depletion, especially in the heart which has low de novo purine nucleotide synthesis.

The course of the reaction sequence hypoxanthine leads to xanthine leads to uric acid, catalysed by the NAD+-dependent activity of xanthine oxidoreductase, was investigated under conditions either of immediate oxidation of the NADH formed or of NADH accumulation. The enzymic preparation was obtained from rat liver, and purified 75-fold (as compared with the 25000 g supernatant) on a 5'-AMP-Sepharose 4B column; in this preparation the NAD+-dependent activity accounted for 100% of total xanthine oxidoreductase activity. A spectrophotometric method was developed for continuous measurements of changes in the concentrations of the three purines involved. The time course as well as the effects of the concentrations of enzyme and of hypoxanthine were examined. NADH produced by the enzyme lowered its activity by 50%, resulting in xanthine accumulation and in decreases of uric acid formation and of hypoxanthine utilization. The inhibition of the Xanthine oxidoreductase NAD+-dependent activity by NADH is discussed as a possible factor in the regulation of IMP biosynthesis by the 'de novo' pathway or (from unchanged hypoxanthine) by ther salvage pathway.

Background: The paper presents the Nofer Institutes of Occupational Medicine in Łódź's results of the assessment of individual dose equivalents Hp(0.07) of medical staff exposed to X-rays in Poland in 2012. In addition, the collected data was analysed in terms of types of medical units performing medical procedures and the categorization of personnel. Material and Methods: Dosimetric service was provided for medical staff of interventional radiology departments occupationally exposed to ionizing radiation in terms of individual dose equivalents Hp(0.07). In 2012, personal dosimetry Hp(0.07) determinations were performed by the Nofer Institute of Occupational Medicine in Łódź and covered 2044 employees from 174 health facilities. The determinations were performed using thermoluminescence dosimetry according to the procedure accredited by the Polish Centre for Accreditation (document number AB 327). The measurements were performed using ring-dosimeters in the periods of 1 or 2 months. Results: Mean annual individual dose equivalent Hp(0.07) in 2012 was equal to 3.3 mSv (annual limit for Hp(0.07) is 500 mSv). The average value of annual individual dose equivalent Hp(0.07) decreased comparing to the previous year. In 2012, no single case of exceeding the annual limit for Hp(0.07) was reported. Data stored in the file indicates that more than 96% of all of the annual doses did not exceed the level of 10 mSv. Conclusions: The analysis of data on occupational exposure to ionizing radiation confirms a stable level of exposure and satisfactory radiological protection in interventional radiology facilities monitored by the Nofer Institute of Occupational Medicine in Łódź in

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