Evidence for involvement of medium chain acyl-CoA dehydrogenase in the metabolism of phenylbutyrate.

Abstract

Sodium phenylbutyrate is used for treating urea cycle disorders, providing an alternative for ammonia excretion. Following conversion to its CoA ester, phenylbutyryl-CoA is postulated to undergo one round of β-oxidation to phenylacetyl-CoA, the active metabolite. Molecular modeling suggests that medium chain acyl-CoA dehydrogenase (MCAD; EC 1.3.99.3), a key enzyme in straight chain fatty acid β-oxidation, could utilize phenylbutyryl-CoA as substrate. Moreover, phenylpropionyl-CoA has been shown to be a substrate for MCAD and its intermediates accumulate in patients with MCAD deficiency. We have examined the involvement of MCAD and other acyl-CoA dehydrogenases (ACADs) in the metabolism of phenylbutyryl-CoA. Anaerobic titration of purified recombinant human MCAD with phenylbutyryl-CoA caused changes in the MCAD spectrum that are similar to those induced by octanoyl-CoA, its bona fide substrate, and unique to the development of the charge transfer ternary complex. The calculated apparent dissociation constant (K(D app)) for these substrates was 2.16 μM and 0.12 μM, respectively. The MCAD reductive and oxidative half reactions were monitored using the electron transfer flavoprotein (ETF) fluorescence reduction assay. The catalytic efficiency and the K(m) for phenylbutyryl-CoA were 0.2 mM 34(-1)·sec(-1) and 5.3 μM compared to 4.0 mM(-1)·sec(-1) and 2.8 μM for octanoyl-CoA. Extracts of wild type and MCAD-deficient lymphoblast cells were tested for the ability to reduce ETF using phenylbutyryl-CoA as substrate. While ETF reduction activity was detected in extracts of wild type cells, it was undetectable in extracts of cells deficient in MCAD. The results are consistent with MCAD playing a key role in phenylbutyrate metabolism.

• Authors: Kaitlyn Kormanik, Heejung Kang, Dean Cuebas, Jerry Vockley, Al-Walid Mohsen
• Journal: Molecular genetics and metabolism (Mol Genet Metab) Vol. 107 Issue 4 Pg. 684-9 (Dec 2012) ISSN: 1096-7206 [Electronic] United States
• PMID: 23141465 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2012 Elsevier Inc. All rights reserved.

Chemical References

• Electron-Transferring Flavoproteins
• Phenylbutyrates
• Recombinant Proteins
• Acyl-CoA Dehydrogenase

Topics

• Acyl-CoA Dehydrogenase (chemistry, metabolism)
• Catalytic Domain
• Electron-Transferring Flavoproteins (metabolism)
• Humans
• Kinetics
• Metabolic Networks and Pathways
• Molecular Docking Simulation
• Oxidation-Reduction
• Phenylbutyrates (metabolism)
• Protein Conformation
• Recombinant Proteins (metabolism)
• Substrate Specificity