[Oligomerization of phenylalanine hydroxylase during its activation with phenylalanine]

Activated and nonactivated forms of phenylalanine hydroxylase varied in the activity within the first minutes of the reaction initiated by means of a synthetic coenzyme 6,7-dimethyl-5,6,7,8-tetrahydropteridine. In activation of the enzyme by phenylalanine the degree of its oligomerization was altered. As shown by chromatography and ultracentrifugation nonactivated enzyme was a dimer with molecular mass 130,000 daltons, whereas the activated form was found to be tetramer of 260,000 daltons. H and L subunits of phenylalanine hydroxylase were equally important in organization of the tetramer. Activation of phenylalanine hydroxylase altered the enzyme affinity to hydroxyapatite. Thus, allosteric activation of phenylalanine hydroxylase occurred due to the enzyme oligomerization.