Dietary restriction and triiodothyronine (T₃) regulation of malate-aspartate shuttle enzymes in the liver and kidney of mice

Abstract

The activities of malate-aspartate shuttle enzymes viz., cytosolic and mitochondrial aspartate aminotransferase (c- and m-AsAT) and malate dehydrogenase (c- and m-MDH) were measured in liver and kidney of ad libitum (AL) and dietary- restricted (DR) mice and also on triiodothyronine (T₃) treatment. The results show that the activity (U/mg protein) of c-AsAT is increased significantly in liver and the activities of c-MDH and m-AsAT are increased significantly in kidney during DR. On T₃ treatment, the activities of both the isoenzymes (c- and m-) of MDH and AsAT are increased significantly in the liver of AL- and DR-fed mice. In the kidney, m-MDH showed no effect by T₃ treatment, however, c-MDH increased significantly in both AL- and DR-fed mice. In contrast, m-AsAT is increased significantly in the kidney in AL-fed mice, but was not affected in DR-fed animals. In vitro reconstitution of malate-aspartate shuttle showed a higher activity in the liver and kidney of DR-fed mice, as compared to AL-fed ones and also in the T₃-treated mice, compared to untreated ones. These findings suggest that malate-aspartate shuttle enzymes are differentially regulated during DR in mice, in order to adapt to the metabolic need of liver and kidney. T₃ potentially regulates the shuttle enzymes, albeit to a varying degree in the liver and kidney of AL- and DR-fed mice.