Further Studies of Dopamine Metabolism and Function in Tetrahymena1

The large amounts of dopamine accumulated by cells of Tetrahymena pyriformis strain NT-1 and secreted into their growth medium were found to depend primarily upon an extracellular, non-enzymatic conversion of tyrosine to L-dihydroxyphenylalanine (L-DOPA); L-DOPA was then rapidly taken into the cells and transformed into dopamine enzymatically. Efforts to find physiologically significant dopamine binding sites on the cell surface or dopamine-sensitive adenylate cyclase activity were unsuccessful, suggesting that the catecholamine does not function in Tetrahymena as it does in higher animals.