5-Ethynyluracil is a time-dependent and tight binding inhibitor of xanthine oxidase. The maximal value of the first-order rate constant for onset of inhibition is 0.01 s-1, and the concentration of 5-ethynyluracil which gives one-half of this value is 190 microM. Because the t1/2 for formation of active enzyme from inhibited enzyme is greater than 30 h in the absence of NADH, inhibition of xant...

The reduction of cytochrome c by xanthine oxidase and the competitive inhibition of this process by carbonic anhydrase and by myoglobin have been studied by kinetic and by equilibrium binding methods. Carbonic anhydrases isolated from bovine and from human erythrocytes differed strikingly in their ability to inhibit competitively the reduction of cytochrome c. The KS for cytochrome c was a func...

In 1948 Miller (1) demonstrated that the loss of liver xanthine oxidase activity in the rat greatly exceeded the loss of liver protein during acute inanition. Moreover, xanthine oxidase appeared to be the most labile of the four liver enzymes studied. Westerfeld and Richert (2) observed that increasing the level of protein in the diet tended to bring about an increase in liver xanthine oxidase ...

A major development over the past two decades has been the realization that free radical induced lipid peroxidation and DNA damage are associated with major health problems, e.g. cancer and ageing. Plant-derived antioxidants are increasingly found beneficial in protecting against these diseases. Celtis australis L. and Celtis occidentalis L. are two plants that have a variety of uses in folk me...

Xanthine oxidase is a key enzyme which can catalyze hypoxanthine and xanthine to uric acid causing hyperuricemia in humans. Xanthine oxidase inhibitory activities of 24 organic extracts of four species belonging to Citrus genus of the family Rutaceae were assayed in vitro. Since the ethyl acetate extract of C. aurantium dried immature fruits showed the highest xanthine oxidase inhibitory activi...

Oxidative endothelial dysfunction is a critical initiator of vascular disease. Vitamin E is an effective antioxidant but attempts to use it to treat vascular disorders have been disappointing. This study investigated whether tocotrienols, the less abundant components of vitamin E compared to tocopherols, might be more effective at preserving endothelial function. Superoxide generated by hypoxan...

To assay the in vitro xanthine oxidase and Tyrosinase inhibitory activity of the alkaloid fractions of the leaves of Indigofera spalathoides and to determine its enzyme inhibition mechanism. Xanthine oxidase and Tyrosinase inhibitory activity was assayed spectrophotometrically under aerobic conditions and the degree of enzyme inhibition was determined by measuring the increase in absorbance at ...

Alcohol consumption increases the risk for breast cancer in women by still undefined means. Alcohol metabolism is known to produce reactive oxygen species (ROS), and breast cancer is associated with high levels of hydroxyl radical (OH) modified DNA, point mutations, single strand nicks, and chromosome rearrangement. Furthermore, ROS modification of DNA can produce the mutations and DNA damage f...

The quinimine form of p-aminophenol inhibits the oxygen uptake of tissue suspensions and in very small concentrations inhibits specifically the oxidation of hypoxanthine and xanthine to uric acid by the xanthine oxidase of liver (1). Closely related compounds such as o-aminophenol, p-phenylenediamine, and quinone, although they inhibit to different degrees the oxygen uptake of tissues, have no ...