HEPATIC AND RENAL D-AMINO-ACID OXIDASE ACTIVITIES IN THE GROWING RAT AFTER 10 DAYS OF PROTEIN UNDERNUTRITION AND REFEEDING

The activity levels of hepatic and renal D-amino acid oxidase (EC 1.4. 3.3), a key enzyme for D-amino acid utilization in mammals, were deter mined in growing rats after a 10 day period of protein undernutrition and subsequent refeeding. Reducing the protein intake for 10 days (3% casein diet) resulted in an 8% loss of the animals' mean body weight a nd a 50% decrease in the mean size of the liver and kidney as compared to the control animals fed on a 22% casein diet during the same perio d. When the undernourished rats were refed with the normal protein die t, their weight increased about four fold as compared with that of the control animals, and after a ten day period of refeeding, the lost bo dy and tissue weights were completely recovered. As far as the specifi c activity of D-amino acid oxidase was concerned, a 44% reduction took place in the liver of rats subjected to protein undernutrition for 10 days. During the period of refeeding, however, the enzyme activity le vel increased slowly in comparison with the overall hepatic protein le vel, since its specific activity on day 10 was still 28% below that of the control rats. In sharp contrast, no significant change in the kid ney enzyme level was observed throughout these nutritional manipulatio ns. This study strongly suggests that the synthesis and/or catabolism of D-amino acid oxidase may depend on the dietary protein content of t he liver but not on that of the kidney. This suggests that D-amino aci d oxidase may possibly play distinct physiological roles in these two body organs.