noun

• 1Biochemistry
  A crystalline compound found in blood and urine which is an intermediate in the metabolic breakdown of nucleic acids to uric acid.

  A purine derivative; chemical formula: C₅H₄N₄O₂

  ‘Xanthine oxidase catalyses the oxidation of xanthine and hypoxanthine to uric acid and is a well-known producer of superoxide radicals.’

  More example sentences

  • ‘It appears that the purine metabolic system in humans has found a way to avoid the overproduction of uric acid by downregulating the Xor gene expression, the product converting hypoxanthine to xanthine and further xanthine to uric acid.’
  • ‘Xanthine oxidase activity was evaluated by the spectrophotometric measurement of the formation of uric acid from xanthine.’
  • ‘Stones can be composed of calcium, oxalate, urate, cystine, xanthine, phosphate, or all of these.’
  • ‘Red beets, another highly colored vegetable, get their scarlet color from a combination of the purple pigment cyanin and the yellow pigment xanthin.’

  1. 1.1count noun Any of the derivatives of xanthine, including caffeine and related alkaloids.
     ‘Methyl xanthines (caffeine, theophylline and theobromine) are found in seeds and leaves of a variety of unrelated plant species, including coffee, tea, cocoa, cola and mate.’
     More example sentences

     • ‘Ephedrine and the xanthines, such as caffeine and theophylline, increase metabolic rate.’
     • ‘The main components of this tea are natural xanthines such as caffeine, theobromine, theophylline and tanni.’
     • ‘Ice cream gives a little calcium, and chocolate offers plant chemicals called xanthins that can be healthful in moderation.’
     • ‘From that time forward into the present, methyl xanthines have been used, most often in the form of theophylline or the water-soluble, related compound aminophylline, for the treatment of asthma.’