Two variants of ornithine decarboxylase activity in the mouse liver. The nature of enzyme induction

: Ornithine decarboxylase activity in mouse liver is predominantly located in the cell nuclei. After injection of some inducing agents (thioacetamide, diethylnitrosamine, hydrocortisone) the enzyme leaves the nucleus for cytosol. A circadian rhythm of ornithine decarboxylase activity has been observed in nucleus and cytosol, the decrease of enzyme activity in the nucleus being accompanied by its increase in cytosol. The enzyme obtained from intact mice with a minimal level of ornithine decarboxylase activity in the cytosol differs in ion-exchange properties, pH-optimum and Km for ornithine from the thioacetamide stimulated (nucleus enzyme).