Abstract
Dietary protein depletion results in a decrease in rat hepatic xanthine oxidase activity to about 10% of control levels. Refeeding of a high protein diet leads, after a 6-hour lag phase, to a 5-fold increase in enzyme activity by 12 hours. The mechanism of this increase was studied utilizing actinomycin D, 5-fluorouracil, and puromycin. These agents all blocked the increase in enzyme activity, indicating that both ribonucleic acid and protein syntheses were involved. Following administration of 14C-leucine, specific radioactivities of xanthine oxidase were identical in the livers of protein-depleted and control animals, despite a 10-fold difference in enzyme activity levels. These results indicated that the fractional turnover rates were the same in the two groups of rats and suggested that the rate of xanthine oxidase synthesis was reduced 10-fold in the depleted rats prior to protein re-feeding. Greatly increased isotopic labeling of highly purified enzyme with 14C-leucine during the phase of restoration of enzyme levels indicated that the increase in activity was the result of accelerated apoenzyme synthesis de novo.
Highlights
Refeeding of a 23% protein diet resulted in a rise of activity to levels about 55% of control levels in 12 hours
There was an initial 6-hour lag period followed by a rapid rise between 6 and
RNA, was evaluated. 5-Fluorouracil was given intraperitoneally in a dose of 50 mg hourly, commencing at the time of refeeding, according to the technique of Garen et al, and its administration was associated with a complete inhibition of the usual rise of enzyme activity found at 12 hours after refeeding. These results indicated that the rise of xanthine oxidase activity associated with refeeding is dependent upon new RNA
Summary
Female Osborne Mendel rats, 10 to 11 weeks old, weighing 170 to 200 g, were used in all experiments. These animals had been maintained exclusively on standard Purina rat chow (23% protein) from weaning. The rats were housed five to a cage, and for 14 days each received approximately 14 g of 8% low protein diet. The diet contains salt mixture USP XIV and Vitamin Diet Fortification Mixture (Nutritional Biochemicals). On this regimen the animals gained 5 to 10% of their original weight over 14 days compared with a 10 to 15% gain for control animals maintained on standard Purina rat chow. Refeeding was carried out with Purina rat Studies on Xanthine Oxidase
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
