On the Mechanism of Lactate Dehydrogenase Leakage from Normal and D-Galactosamine-Treated Hepatocytes in Monolayer Culture

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Abstract
Synthesis, degradation and leakage of lactate dehydrogenase [LD] and of total protein was measured using D-galactosamine-treated rat hepatocytes in monolayer culture. The kinetics of [3H]leucine incorporation into trichloroacetic acid-precipitable material and into isolated LD of cells and of the extracellular space revealed a similar extent of inhibition of both synthesis and leakage following exposure to D-galactosamine. Hepatocyte cultures that had been labeled before D-galactosamine treatment lost intracellular protein-associated radioactivity almost as rapidly as control cells up to the time of measurable enzyme leakage; thereafter, the rate of 3H-loss increased in the treated cells. LD present in the medium is degraded less rapidly than the enzyme in the intracellular space. This explains the apparent increase of total LD activity in D-galactosamine-treated as compared to control cultures. Following [3H]leucine addition to D-galactosamine-treated cultures, the specific radioactivity of the leaked LD in the medium was never greater than that of the enzyme in the cytosolic compartment. The data rule out a direct excretion of newly synthesized enzyme as a result of D-galactosamine action.