Some kinetic properties of Mucor rouxii phosphofructokinase. Effect of cyclic adenosine 3', 5'-monophosphate.

Intact and pure parenchymal and nonparenchymal cells were isolated from rat liver. The activities of Superoxide dismutase in these cell types were determined by two different methods. With both methods the specific activity of this enzyme is 1.5 times higher in parenchymal than in nonparenchymal liver cells. It can be calculated that about 7% of the total rat liver Superoxide dismutase activity is localized in the nonparenchymal liver cells. Electrophoresis on polyacrylamide gels indicates that the isolated parenchymal cells contain both cytosolic and mitochondrial isoenzymes, whereas with nonparenchymal cells only the cytosolic enzyme could be detected. The mitochondrial band observed in isolated parenchymal cells is absent in the original total liver homogenate. This isoenzyme seems to be activated during the parenchymal cell isolation procedure. Isoelectrofocusing indicates that the cytosolic Superoxide dismutase consists in four different isoelectric forms in both parenchymal and nonparenchymal cells. With the mitochondrial isoenzyme two bands are obtained. The possibility that O₂^? is an important intermediate in H₂O₂ formation in nonparenchymal liver cells is discussed. In this respect, Superoxide dismutase might not only protect the cell against a toxic reagent as O₂^t-, but might also help to regulate the level of the important antimicrobial agent, H₂O₂.