J. Biol. Chem., Vol. 262, Issue 34, 16470-16475, 12, 1987
Activation of rat caudate tyrosine hydroxylase phosphatase by tetrahydropterins
TJ Nelson and S Kaufman
Laboratory of Neurochemistry, National Institute of Mental Health, Bethesda, Maryland 20892.
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.
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