TH and Parkinson disease: To examine whether TH catalyzes the hydroxylation of tyrosine residues in αSyn, we first performed an in vitro reaction assay (Supplementary Fig. 1a) using recombinant TH (enzymatic activity: 624 units/mg)29 with wild-type αSyn or two mutant forms of familial PD, E46K and A53T, characterized by promoting fibril formation30,31.