What is it about?

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-Lcysteine 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 α-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.

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Why is it important?

This is the first reports of the S-oxidation of S-carboxymethyl-L-cysteine in mice.

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This page is a summary of: Mouse recombinant phenylalanine monooxygenase and theS-oxygenation of thioether substrates, Journal of Biochemical and Molecular Toxicology, March 2009, Wiley, DOI: 10.1002/jbt.20274.
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