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Xenobiotica
the fate of foreign compounds in biological systems
Volume 40, 2010 - Issue 5
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General Xenobiochemistry

Post-translational activation of human phenylalanine 4-monooxygenase from an endobiotic to a xenobiotic enzyme by reactive oxygen and reactive nitrogen species

, , , , , & show all
Pages 319-330 | Received 09 Dec 2009, Accepted 03 Feb 2010, Published online: 15 Mar 2010
 

Abstract

  1. An investigation into the post-translational activation of cDNA-expressed human phenylalanine 4-monooxygenase and human hepatic cytosolic fraction phenylalanine 4-monooxygenase activity with respect to both endobiotic metabolism and xenobiotic metabolism revealed that the reactive oxygen species (hydrogen peroxide and hydroxyl radical) and reactive nitrogen species (nitric oxide and peroxynitrite) could elicit the post-translational activation of the enzyme with respect to both of these biotransformation reactions.

  2. In virtually all instances, the Km values were decreased and the Vmax values were increased; the only exceptions observed being with hydrogen peroxide and L-phenylalanine.

  3. These effects were shown to occur at activator concentrations known to exist in physiological situations and, hence, suggest that reactive oxygen and reactive nitrogen species may cause, and may be involved with, the post-translational activation of phenylalanine 4-monooxygenase within the human body.

  4. This mechanism, in response to free-radical bursts, may enable the enzyme to expand its substrate range and to process certain xenobiotics as and when required.

Acknowledgements

This project was funded by project grants from the Thai Royal Government (G. B. S.) and Vetrin SA, Greece (G. B. S.).

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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