RESUMO
Rat tyrosine hydroxylase is phosphorylated at four serine residues, at positions 8, 19, 31, and 40 in its amino terminal regulatory domain by multiple protein kinases. Cyclic AMP-dependent protein kinase phosphorylates S40, which results in alleviation of inhibition by dopamine. Extracellular signal-regulated protein kinase 2 phosphorylates S8 and S31. Site-directed serine-to-glutamate mutations were introduced into tyrosine hydroxylase to mimic prior phosphorylation of the regulatory serines; these proteins were used as substrates for cAMP-dependent kinase and extracellular signal-regulated kinase 2. The activity of cAMP-dependent kinase was unaffected by the substitution of serines 8, 19 or 31 with glutamate and the activity of extracellular signal-regulated kinase 2 was unaffected by substitution of serines 19 or 40 with glutamate. Cyclic AMP-dependent kinase was less active in phosphorylating S40 if dopamine was bound to tyrosine hydroxylase, but extracellular signal-regulated kinase 2 phosphorylation at S31 was unaffected by the presence of dopamine.