RAPID TURNOVER OF TRYPTOPHAN-HYDROXYLASE IN SEROTONIN PRODUCING CELLS- DEMONSTRATION OF ATP-DEPENDENT PROTEOLYTIC DEGRADATION

A rapid and continuous proteolysis of tryptophan hydroxylase was demon strated with two mast cell lines derived from rat basophilic leukemia cells (RBL2H3) and mouse mastocytoma (FMA3). Under conditions in which protein biosynthesis was arrested by administration of cycloheximide, the decay profile of tryptophan hydroxylase protein was traced by Wes tern blot analysis, Incorporation of [S-35]methionine and the chase ex periment performed without interfering with the metabolic stage also s howed that tryptophan hydroxylase had been cleaved rapidly, The half l ife of the enzyme was 11-15 min in RBL2H3 cells and 40-60 min in FMA3 cells, and the process was demonstrated to be dependent on intracellul ar ATP.