Studies on the Degradation of Tyrosine Aminotransferase in Hepatoma Cells in Culture

Abstract

The degradation of glucocorticoid-induced tyrosine amino-transferase and of general cellular proteins in hepatoma (HTC) cells in culture is by the deprivation of both amino acids and of serum, and by lowering the pH of the medium. This enhanced degradation, but not the normal degradation, is inhibited by inhibitors of protein synthesis. Sodium fluoride and other inhibitors of cellular ATP production profoundly inhibit the degradation of tyrosine aminotransferase and other proteins. This effect was shown, in the case of tyrosine aminotransferase, to be rapidly reversible and exerted by a mechanism different from the inhibition of protein synthesis. It is proposed that ATP participates in an early phase of enzyme degradation.