title: Rat liver phenylalanine hydroxylase. Activation by sulfhydryl modification.
abstract: Upon reaction with N-ethylmaleimide, a single sulfhydryl residue/Mr = 50,000 subunit of phenylalanine hydroxylase is modified. This modification is accompanied by a 20-30-fold increase in hydroxylase activity when the activity is measured with tetrahydrobiopterin as cofactor. The N-ethylmaleimide-modified enzyme exhibits many of the characteristics of phenylalanine hydroxylase activated by partial proteolysis or by exposure to phospholipids. For example, a change from sigmoid to hyperbolic kinetics with varying phenylalanine concentration is observed, in addition to broadened substrate specificity and a dependence on phenylalanine hydroxylase stimulator protein at pH 6.8. The binding of phenylalanine to phenylalanine hydroxylase in the absence of pterin cofactor has also been studied. The native enzyme exhibits a sigmoidal phenylalanine binding curve. The N-ethylmaleimide-modified enzyme shows a hyperbolic response to phenylalanine binding in addition to an apparent decrease in total phenylalanine binding.
mesh_terms: D000818:Animals; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D005033:Ethylmaleimide / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats
chemical_list: D008244:Lysophosphatidylcholines; D010649:Phenylalanine; D004228:Dithionitrobenzoic Acid; D010651:Phenylalanine Hydroxylase; D005033:Ethylmaleimide