Glutamate Dehydrogenase of Nuclear and Extra‐Nuclear Compartments of Chang's Liver Cells

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Abstract
Glutamate dehydrogenase activity is present in both the nuclear and mitochondrial fractions of Chang's liver cells. After solubilization, the two activities were shown to differ from each other in response to variation of pH, in the stimulating effect of anions, especially inorganic phosphate, in response to variation of the concentration of NAD+, and in the ratio of velocities obtained with saturating concentrations of NADH and NADPH. During the 4‐day growth cycle of Chang's liver cells, glutamate dehydrogenase activity in nuclei attained a maximal activity of 4‐ to 7‐fold the starting value, within 12–16 hours after incubation in fresh growth medium. Glutamate dehydrogenase in the extra‐nuclear fraction required 24 hours to reach its maximal activity level of about 150% of the initial value. Incubation of cells in a medium lacking an essential amino acid resulted in a significant decrease of glutamate dehydrogenase activity of the extra‐nuclear compartment, but no change in the nuclear activity. It is concluded that two glutamate dehydrogenases are present in Chang's liver cells and that they may have different functions.