title: Suppression of rabbit myocardial xanthine dehydrogenase activity by an endogenous compound.
abstract: Xanthine dehydrogenase (XDH) is an important precursor to the oxygen radical producing enzyme xanthine oxidase (XO). We found that the apparent activity of rabbit myocardial XDH increased from 2 +/- 1 to 50 +/- 3 microU/g (P < 0.05) following extraction of tissue homogenate with butanol. Further studies suggested that the basis for this observation was a high molecular weight compound which consumes the XDH cofactor, NAD+. Addition of myocardial homogenate to exogenous NAD+ resulted in depletion of NAD+ and concomitant formation of an additional compound (peak A). Both NAD+ consumption and peak A formation were abrogated by prior extraction of homogenate with butanol. Separation of myocardial homogenate by Sephadex chromatography revealed a high molecular weight compound which suppressed activity of purified milk XDH but not xanthine oxidase (XO). This activity co-eluted with the ability of myocardial homogenate to consume added NAD+ and form peak A. The NAD(+)-consuming activity was heat and acid-labile. In addition, nicotinamide was both a product and an inhibitor of the NADase activity, consistent with the existence of a previously described myocardial glycohydrolase. Extraction of tissue with butanol may be necessary to detect low levels of XDH activity in vitro.
authors.affiliation: Webb-Waring Lung Institute, University of Colorado Health Sciences Center, Denver 80262.
authors.forename: L S
authors.initials: LS
authors.lastname: Terada
mesh_terms: D000818:Animals; D000440:Butanols; D066298:In Vitro Techniques; D008892:Milk / Q000201:enzymology; D008970:Molecular Weight; D015428:Myocardial Reperfusion Injury / Q000517:prevention & control; D009206:Myocardium / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D011817:Rabbits; D014968:Xanthine Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000440:Butanols; D009243:NAD; D014968:Xanthine Dehydrogenase; D014969:Xanthine Oxidase