title: Activation of rat caudate tyrosine hydroxylase phosphatase by tetrahydropterins.
abstract: Tyrosine hydroxylase phosphatase activity in rat caudate nucleus was separated into three peaks by chromatography on DEAE-cellulose. [32P]Tyrosine hydroxylase phosphorylated by cyclic AMP-dependent protein kinase was dephosphorylated only by the major peak eluting at 0.3 M NaCl, while tyrosine hydroxylase phosphorylated by Ca2+-calmodulin-dependent protein kinase was also dephosphorylated by two calcium-inhibited phosphatases. The Vmax of the enzyme in the major DEAE peak was increased by 10 microM tetrahydrobiopterin (BH4) from 0.78 to 5.0 fmol min-1 mg-1 while the Km was only slightly affected, increasing from 45 to 62 pM. The activation could not be reversed by dilution. On Sephadex G-200, the enzyme was found to consist of two major forms with molecular masses of 420 and 100 kDa. In contrast to the activation of liver phosphatases by freezing with beta-mercaptoethanol, activation by tetrahydrobiopterin was not associated with a shift in the molecular weight of the phosphatase to lower molecular weight forms. Other reduced pterins, including tetrahydroneopterin, 6-methyltetrahydropterin, and 5-methyltetrahydrofolate, also activated the enzyme, while oxidized pterins had no effect. GTP, the metabolic precursor of tetrahydrobiopterin, was a potent inhibitor of the phosphatase reaction, inhibiting by 65% at a concentration of 1 microM. These findings suggest a close regulatory interrelationship between the tetrahydrobiopterin synthetic pathway and catecholamine biosynthesis.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002421:Caudate Nucleus / Q000187:drug effects / Q000201:enzymology*; D004789:Enzyme Activation; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D011622:Pterins / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D011622:Pterins; C011552:tetrahydropterin; D006861:Hydrogen Peroxide; D014446:Tyrosine 3-Monooxygenase; D002118:Calcium