Further Studies of Dopamine Metabolism and Function inTetrahymena1

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Abstract
The large amounts of dopamine accumulated by cells of T. pyriformis strain NT-1 and secreted into their growth medium were found to depend primarily upon an extracellular, nonenzymatic 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 Tetrahyemena as it does in higher animals.