Comparison of rat and mouse ornithine aminotransferase with respect to molecular properties and regulation of synthesis

A comparative study of the synthesis patterns and molecular properties of mouse and rat ornithine aminotransferase (OAT) was conducted. The two enzymes were found to be very similar with respect to catalytic properties, two-dimensional electrophoresis patterns of tryptic digests, amino acid compositions, and antibody cross-reactivity. In vitro translation assays for OAT synthesis on free polysomes isolated from livers at different times of day showed similar circadian fluctuations in OAT synthesis for both species. However, hybridization measurements revealed no circadian changes in the levels of hybridizable OAT mRNA in these livers. These results demonstrate that the circadian cycling of OAT synthesis is regulated at the level of translation in both the rat and the mouse.