title: Activation and inactivation of striatal tyrosine hydroxylase: the effects of pH, ATP and cyclic AMP, S-adenosylmethionine and S-adenosylhomocysteine.
abstract: The activity of tyrosine hydroxylase (TH) in the corpus striatum of haloperidol treated and control rats has been examined. The activation of TH by haloperidol caused a decrease in the Km for tetrahydrobiopterin but no change in the Vmax. This effect was totally abolished when homogenates were prepared at high values of pH. A similar activation could be produced in vitro by preincubating with S-adenosylmethionine; conversely, enzyme activity was reduced by preincubating with S-adenosylhomocysteine. ATP and cyclic AMP activated the enzyme when incubated together with TH in vitro but the activity was reduced when the enzyme was preincubated with these substances. A possible role for carboxymethylation in controlling tyrosine hydroxylase activity is discussed.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003342:Corpus Striatum / Q000201:enzymology*; D000242:Cyclic AMP / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006220:Haloperidol / Q000494:pharmacology; D006710:Homocysteine / Q000031:analogs & derivatives*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051381:Rats; D011919:Rats, Inbred Strains; D012435:S-Adenosylhomocysteine / Q000494:pharmacology*; D012436:S-Adenosylmethionine / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D006710:Homocysteine; D012436:S-Adenosylmethionine; D000255:Adenosine Triphosphate; D012435:S-Adenosylhomocysteine; D000242:Cyclic AMP; D014446:Tyrosine 3-Monooxygenase; D006220:Haloperidol