PPP1R1B and Parkinson disease: 12 Similarly, the overexpression of synaptic vesicular amine transporter in neuronal cell cultures, treated with l-DOPA which is rapidly converted to DA, inhibited the synthesis of NM by lowering the cytosolic concentration of DA.10 It is noteworthy that the protein phosphatase 1 regulatory subunit 1B, that we found in all samples, is involved in l-DOPA induced dyskinesia in PD.