Phosphorylation and activation of brain aromatic L-amino acid decarboxylase by cyclic AMP-dependent protein kinase

Aromatic L-amino acid decarboxylase (AAAD), an enzyme required for the synt hesis of catecholamines, indoleamines, and trace amines, is rapidly activat ed by cyclic AMP-dependent pathways in striatum and midbrain in vivo, sugge sting enzyme phosphorylation. We now report that the catalytic subunit of c yclic AMP-dependent protein kinase (PKA) directly phosphorylated AAAD immun oprecipitated from homogenates prepared from the mouse striatum and midbrai n in vitro. Under the same phosphorylation conditions, the catalytic subuni t of PKA also phosphorylated a recombinant AAAD protein expressed in Escher ichia coli transfected with an AAAD cDNA isolated from the bovine adrenal g land. The PKA-induced AAAD phosphorylation of immunoprecipitates from stria tum and midbrain was time and concentration dependent and blocked by a spec ific PKA peptide inhibitor. Incubation of the catalytic subunit of PKA with striatal homogenates increased enzyme activity by similar to 20% in a time - and concentration-dependent manner. Moreover, incubation of the catalytic subunit of PKA with recombinant AAAD increased activity by similar to 70%. A direct phosphorylation of AAAD protein by PKA might underlie the cyclic AMP-induced rapid and transient activation of AAAD in vivo.