Mouse recombinant phenylalanine monooxygenase and the S-oxygenation of thioether substrates.
The substrate specificity of mouse recombinant phenylalanine monooxygenase (mPAH) has been investigated with respect to the mucoactive drug, S-carboxymethyl-L-cysteine (SCMC) and its thioether metabolites. Phenylalanine monooxygenase was shown to be able to catalyze the S-oxygenation of SCMC, its decarboxylated metabolite, S-methyl-L-cysteine and both their corresponding N-acetylated forms. However, thiodiglycolic acid was found not to be a substrate. The enzyme profiles for both phenylalanine and SCMC showed Michaelis-Menten with noncompetitive substrate inhibition for both the substrate-activated and the lysophosphatidylcholine-activated mPAH assays. The tetrameric enzyme was shown to undergo posttranslational activation by preincubation with substrate, lysophosphatidylcholine, N-ethylmaleimide (a thiol alkylating agent), and the proteolytic enzymes alpha-chymotrypsin and trypsin. Similar posttranslational activation of PAH activity in the rat and human has also been reported. These results suggest that in the mouse, PAH was responsible for the S-oxidation of SCMC and that the mouse models of the hyperphenylalaninemias may be a potential tool in the investigation of the S-oxidation polymorphism in man.
King's College London, Pharmaceutical Science Division, School of Biomedical and Health Sciences, London, United Kingdom. glyn.steventon@kcl.ac.uk
Glyn B
GB
Steventon
Stephen C
SC
Mitchell
D000818:Animals; D004789:Enzyme Activation; D007700:Kinetics; D051379:Mice; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010651:Phenylalanine Hydroxylase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism; D013440:Sulfides / Q000378:metabolism*
D011994:Recombinant Proteins; D013440:Sulfides; D010651:Phenylalanine Hydroxylase; D010100:Oxygen