STABILITY OF SOME ENZYMES IN CULTURED CELLS

The effect of inhibitors of protein synthesis on the activity of 3 enzymes in 2 types of cultured cells-KB cells and rat embryo fibroblasts-was studied. It was found that the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in rat fibroblasts, as well as of glucose-6-phosphate and malate dehydrogenase in KB cells, stays constant for more than 3 days in the presence of either cycloheximide (5-50 μg/ml) or puromycin (0.1-1.0 μg/ml). This means that the three enzymes are stable entities in their environment in cultured cells. The steady state model often employed to describe enzyme regulation in mammalian tissue can thus not apply to these enzymes in cultured cells, and raises some questions regarding the mechanism of their turnover in organs such as the liver. © 1969.