Characteristics of the activation by dithiothreitol and Fe2+ of tryptophan hydroxylase from the rat brain

The preincubation of tryptophan hydroxylase extracted from various areas of the central nervous system of the rat with 30 mM dithiothreitol and 50 M ferrous ammonium sulfate under nitrogen atmosphere resulted in a persistent increase of its activity. Studies on the enzyme characteristics indicated that this activation was associated with a doubling in itsV_max and a shift (from 7.6 to 7.2) of the optimal pH for its activity. In contrast, the molecular weight and the apparent affinities of tryptophan hydroxylase for its pterin cofactor and for tryptophan were not significantly altered by the preincubation with dithiothreitol and ferrous ammonium sulfate. Since this treatment did not prevent the stimulatory effects of various compounds (phosphatidylserine, ATP and Mg²⁺, Ca²⁺) on tryptophan hydroxylase activity, this might be a good procedure to activate this enzyme with only minor changes in its regulatory properties.