Activity of aspartate carbamoyltransferase in ovine tissues

The activity of the enzyme aspartate carbamoyltransferase (ACT; EC 2.1.3.2) was studied in ovine tissues. Hepatic, ileal and duodenal tissues showed higher levels of activity (6-19 units) than skeletal muscle, cardiac muscle, lung, spleen, kidney and rumen wall (2-7 units). Low growth impetus skeletal muscles had higher activity (2.9 units) than high growth impetus muscles (1.8 units) taken from immature sheep but such differences were not present in mature sheep. Refeeding of starved immature and mature sheep resulted in two- to threefold increases in activity of ACT in hepatic, ileal and duodenal tissues. These elevated levels of ACT activity were maintained for considerably longer (100 days in immature and 50 days in mature sheep) than the 30 days required for both groups of sheep to achieve liveweights similar to those of continuously grown animals. The optimum pH for ACT activity from both liver and ileum was between pH 8.5 and 9.2 pH profiles showed that activity of ileal ACT was consistently lower than liver ACT in the pH range 6.0-8.5. Starch-gel electrophoresis indicated only one major band of enzyme activity in both liver and ileum. However, both enzymes migrated to different positions in the gel with ileal ACT being the faster migrating of the enzyme forms.