In advanced cancer patients, the oxidative stress could take place either at the onset of disease or as a function of disease progression. To test this hypothesis, the following parameters were investigated: the erythrocyte activity of the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), the serum activity of glutathione reductase (GR) and the serum total antioxidant status (TAS). The total antioxidant capacity of plasma LMWA was evaluated by the cyclic voltammetry methodology. We further determined the serum levels of proinflammatory cytokines (IL-6 and TNF␣), IL-2, leptin and C-reactive protein (CRP). All of these parameters have been correlated with the most important clinical indices of patients such as Stage of disease, ECOG PS and clinical response. Eighty-two advanced stage cancer patients and 36 healthy individuals used as controls were included in the study. Our findings show that SOD activity was significantly higher in cancer patients than in controls and GPx activity was significantly lower in cancer patients than in controls. Serum values of IL-6, TNF␣ and CRP were significantly higher in patients than in controls. Serum leptin values of cancer patients were significantly lower than controls. SOD activity increased significantly from Stage II/ECOG 0-1 to Stage IV/ECOG 0 -1, whereas it decreased significantly in Stage IV/ECOG 3. GPx activity decreased significantly in Stage IV/ECOG 2-3. An inverse correlation between ECOG PS and serum leptin levels was found. Serum levels of IL-2 decreased from Stage II/ECOG 0 -1 to Stage IV/ECOG 2-3. A direct correlation between Stage/ECOG PS and serum levels of both IL-6 and CRP was observed. Cisplatin administration induced a significant increase of GPx after 24 hr. In conclusion, this is the first study that shows that several "biological" parameters of cancer patients such as antioxidant enzyme activity, cytokines, leptin and CRP strictly correlate with the most important clinical parameters of disease such as Stage and ECOG PS.

The active site of tyrosinase is described with a view to depicting its interactions with substrates and inhibitors. Occurrence and mechanism(s) of tyrosinase-mediated browning of agrofood products are reviewed, with regard to both enzymic and chemical reactions, and their control, modulation, and inhibition. Technical and applicational implications are discussed.

Copper amine oxidases utilize 2,4,5-trihydroxyphenylalanine quinone (topaquinone) as a cofactor in enzymatic catalysis. This cofactor is formed from a tyrosine residue through a self-catalytic mechanism with the participation of the copper ion at the active site. Although pathways have been postulated for topaquinone biogenesis, portions of this scheme are still unclear. We utilized 4-tert-butyl-derived models for the putative intermediates of topaquinone generation and studied the effect of Cu(II) and Zn(II) ions on each autoxidative step from dopa-to topaquinone-like compounds at physiological pH (7.4). Several polyvinyl-alcohol-based soluble resins bearing mono-and di-hydroxyphenolic moieties were also prepared, and their tendency to give hydroxyquinonic structures when incubated at alkaline pH values was investigated. Our results confirm (although indirectly) the formation of dopa and dopaquinone during topaquinone biosynthesis. Moreover, we collected evidence that, following the formation of dopa, the role of the active-site copper ion in topaquinone biogenesis would be limited to the catalysis of the two subsequent quinonization steps (i.e. from dopa to dopaquinone and from topa to topaquinone), thus disfavoring the possibility of a direct intervention of the metal ion in the hydroxylation of dopaquinone. In particular, Cu(II) was shown to influence deeply the autoxidation of 1,2,5-trihydroxy-4-tert-butylbenzene, used as model of topa, both increasing the reaction rate and changing its mechanism. The mechanistic implications of these findings for the biogenesis of topaquinone and its analogs at the active site of various amine oxidases are discussed.

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A protein with NADH oxidase activity from the extreme thermophile Thermus aquaticus YT-1 was purified and characterised. The enzyme was found to have a relative molecular mass of 110000 and be composed of two subunits of identical size. FAD was found to be present at a concentration of 0.7 mol/mol dimer and was required for activity. During the oxidation of NADH, oxygen uptake takes place with the production of hydrogen peroxide. The enzyme had, with the exception of a higher glutamic acid and tryptophan content, a similar amino acid composition as the NADH oxidase isolated from the mesophile Bacillus megaterium. Purified NADH oxidase was found to have a K , of 39 pM for ,!?-NADH and a VmaX of 4.68 pmol NADH mg-min-' and was still active at 95°C. Enzymatic activity was found to be independent of pH between 5.0 and 10.5.