methods used in tyrosine hydroxylase purification and assay were the same as previously reported. 14J5 Tyrosine hydroxylase kinetics were determined by the method of Lineweaver- Burk16 with substrate concentrations varying from 6 X to M and by the method of Dixon17 with substrate concentrations set at 5 x and at 1 X M. DMPH4 concentration was constant in the inhibition studies at 10-3 M but was later varied between 1