21. This activity is often found in a bifunctional enzyme with xanthine oxidase ( ) activity too. 22. Yerba mate contains three xanthines : caffeine, theobromine and theophylline, the main one being caffeine. 23. Xanthine dehydrogenase can be converted to xanthine oxidase by reversible sulfhydryl oxidation or by irreversible proteolytic modification.24. Xanthine dehydrogenase can be converted to xanthine oxidase by reversible sulfhydryl oxidation or by irreversible proteolytic modification. 25. Xanthine dehydrogenase belongs to the group of molybdenum-containing hydroxylases involved in the oxidative metabolism of purines.26. Tea also contains small amounts of theobromine and theophylline, which are stimulants, and xanthines similar to caffeine. 27. "' Caffeine "'is a xanthine alkaloid compound that acts as a stimulant in humans. 28. Enzymes that contain the molybdopterin cofactor include xanthine oxidase, DMSO reductase, sulfite oxidase, and nitrate reductase. 29. However, the inhibitory effect of xanthines on phosphodiesterases are only seen at dosages higher than what people normally consume. 30. The " xpt " gene encodes a specific xanthine phosphoribosyltransferase protein, which is involved in purine metabolism.
