Xanthine

About: Xanthine is a research topic. Over the lifetime, 4046 publications have been published within this topic receiving 129820 citations. The topic is also known as: Xanthine.

Phytic Acid Inhibits Free Radical Formation In Vitro but Does Not Affect Liver Oxidant or Antioxidant Status in Growing Rats

Abstract: The objective of this study was to determine the effects of phytic acid on free radical generation in vitro and in growing rats. Electron spin resonance spectroscopy studies using 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap indicate a complete inhibition of hydroxyl radical formation via the iron-catalyzed Fenton reaction at molar phytic acid/iron ratios >5. However, phytic acid had no scavenging effect on superoxide radicals generated in the xanthine/xanthine oxidase reaction. For the in vivo study, male growing albino rats were fed purified diets based on casein, cornstarch and vitamin E-stripped corn oil differing in the concentration of iron (30 or 300 mg/kg), phytic acid (0 or 10 g/kg) and dl-alpha-tocopheryl acetate (0 or 50 mg/kg). At marginal dietary iron supply, phytic acid supplementation reduced apparent Fe absorption, thereby decreasing liver Fe concentration. Dietary iron and phytate had no effect on the level of hepatic alpha-tocopherol, reduced glutathione, thiobarbituric acid-reactive substances and protein carbonyls. The concentration of thiobarbituric acid-reactive substances and protein carbonyls in the liver decreased as dietary vitamin E was increased from 0 to 50 mg/kg diet. The results obtained provide evidence for antioxidant properties of phytic acid under in vitro conditions. However, neither phytic acid nor iron had any significant effect on liver oxidant or antioxidant status in vivo in growing rats.

Measurement of xanthine oxidase in biological tissues.

Abstract: Publisher Summary This chapter discusses the role of xanthine oxidase in biological tissues. Xanthine oxidase appears to exist in nature in two distinct functional forms, an oxidase (XO) and a dehydrogenase (XD). In addition, xanthine oxidase has a liberal substrate specificity that includes alcohols, aldehydes, and other purines, such as hypoxanthine. The conventional method for determining XO activity involves following the rate of uric acid (UA) formation from xanthine spectrophotometrically at 295 nm in the presence or absence of NAD + . Although this reaction is physiologically relevant and the substrate (xanthine) is highly specific for XO and XD, this procedure is limited by its lack of sensitivity. In addition, other compounds that absorb light at 295 nm may reduce the specificity of the assay. An improved procedure involves incubation of the enzyme with the same substrates, assaying for UA levels by high-performance liquid chromatography (HPLC). This allows for a longer incubation, and hence increasing sensitivity. HPLC analysis also permits the specific determination of UA formation, as NAD + , xanthine, ethylenediaminetetraacetic acid (EDTA), and perhaps other molecules relevant to the assay system all absorb light at 295 nm. The reaction pH of 7.8 is higher than physiologic intracellular pH to increase the sensitivity of the assay, as the pH optima of both XO and XD are 8.0 to 9.0.

Nucleotide sequence of the xanthine guanine phosphoribosyl transferase gene of E. coli

Abstract: The nucleotide sequence of the gpt coding for the enzyme xanthine guanine phosphoribosyl transferase has been determined. The gene codes for a protein of molecular weight 16,950. The construction of deletions in the gpt gene which can be used for the genetic analysis of mutations in the gpt gene, is described.