Rapid turnover of tryptophan hydroxylase in serotonin producing cells: demonstration of ATP‐dependent proteolytic degradation

A rapid and continuous proteolysis of tryptophan hydroxylase was demonstrated 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 Western blot analysis. Incorporation of [35S]methionine and the chase experiment performed without interfering with the metabolic stage also showed that tryptophan hydroxylase had been cleaved rapidly. The half life 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 intracellular ATP.