A possible role for melatonin in regulation of chick liver xanthine dehydrogenase activity

The influence of reserpine on nitrogen metabolizing enzymes in chick liver

Reserpine, a Rauwolfia alkaloid, was shown to increase activity of the hepatic nitrogen metabolizing enzymes xanthine dehydrogenase, purine nucleoside phosphorylase, and tyrosine aminotransferase, when administered orally to young chicks. Using immunochemical techniques, this increase in xanthine dehydrogenase was shown to result from an enhanced de novo enzyme synthesis. The response pattern of the three enzymes to reserpine follows the same pattern to induction by high dietary protein suggesting that a common mode of action may be involved in the regulation of these enzymes. Alpha-Adrenergic blockers, phentolamine and phenoxybenzamine, effectively prevented the increased enzyme activities caused by administration of reserpine.

Synthesis and degradation of xanthine dehydrogenase in chick liver. In vivo and in vitro studies

The present study describes the (xanthine:NAD+ oxidoreductase, EC 1.2.1.37) synthesis and degradation of chick liver xanthine dehydrogenase in vivo and in organ cultures. The results indicate that control of xanthine dehydrogenase activity is mediated by changes in the rate of enzyme synthesis, but that degradation rates are unaffected. The results also suggest that xanthine dehydrogenase synthesis occurs through a previously unreported intermediate. Detected in cultures of liver tissue, this intermediate apparently is not converted into an active enzyme. A model of synthesis and degradation for xanthine dehydrogenase proposes that the synthesis of the enzyme is proportional to messenger RNA and includes an inactive enzyme precursor and a second inactive intermediate prior to degradation. Integrated mathematical solutions describing the concentration of intermediates as a function of time can be found explicitly for simple models. The appendix to this paper extrapolates solutions for one-, two- and three-step models to generate a mathematical solution for an 'n'-step model containing 'n' intermediates. The rate constants in the solutions can be found experimentally.