title: Effect of spermine on tyrosine hydroxylase activity before and after phosphorylation by cyclic AMP-dependent protein kinase.
abstract: The effect of spermine on tyrosine hydroxylase (TH) activity purified from bovine adrenal medulla was examined before and after phosphorylation by the catalytic subunit of cyclic AMP-dependent protein kinase (A-kinase). Before phosphorylation, spermine (less than 1 mM) inhibited the enzymatic activity, and negative cooperative effect of spermine on TH (Hill coefficient = 0.7) was observed from the kinetic analysis concerning 6-methyl-5,6,7,8-tetrahydropterin (6MPH4). Spermine interacted noncompetitively toward tyrosine and the Ki for spermine was calculated to be 68 microM. Phosphorylation abolished the ability of spermine to inhibit TH activity in a negative cooperative manner against the pterin cofactor, and also increased four-fold the Ki value against the substrate. These results suggest that spermine may inhibit TH activity by interacting with the pterin binding site of the enzyme molecule in a manner of negative cooperativity, and that this inhibition is reversed by the conformational change of regulatory domain of TH after phosphorylation by A-kinase.
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D002417:Cattle; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism; D013096:Spermine / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
chemical_list: D011621:Pteridines; D013096:Spermine; D014446:Tyrosine 3-Monooxygenase; D011494:Protein Kinases