Inhibition of N-acetylglutamate synthase by various monocarboxylic and dicarboxylic short-chain coenzyme A esters and the production of alternative glutamate esters.

Abstract

Hyperammonemia is a frequent finding in various organic acidemias. One possible mechanism involves the inhibition of the enzyme N-acetylglutamate synthase (NAGS), by short-chain acyl-CoAs which accumulate due to defective catabolism of amino acids and/or fatty acids in the cell. The aim of this study was to investigate the effect of various acyl-CoAs on the activity of NAGS in conjunction with the formation of glutamate esters. NAGS activity was measured in vitro using a sensitive enzyme assay with ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) product analysis. Propionyl-CoA and butyryl-CoA proved to be the most powerful inhibitors of N-acetylglutamate (NAG) formation. Branched-chain amino acid related CoAs (isovaleryl-CoA, 3-methylcrotonyl-CoA, isobutyryl-CoA) showed less pronounced inhibition of NAGS whereas the dicarboxylic short-chain acyl-CoAs (methylmalonyl-CoA, succinyl-CoA, glutaryl-CoA) had the least inhibitory effect. Subsequent work showed that the most powerful inhibitors also proved to be the best substrates in the formation of N-acylglutamates. Furthermore, we identified N-isovalerylglutamate, N-3-methylcrotonylglutamate and N-isobutyrylglutamate (the latter two in trace amounts), in the urines of patients with different organic acidemias. Collectively, these findings explain one of the contributing factors to secondary hyperammonemia, which lead to the reduced in vivo flux through the urea cycle in organic acidemias and result in the inadequate elimination of ammonia.

• Authors: M Dercksen, L IJlst, M Duran, L J Mienie, A van Cruchten, F H van der Westhuizen, R J A Wanders
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 1842 Issue 12 Pt A Pg. 2510-6 (Dec 2014) ISSN: 0006-3002 [Print] Netherlands
• PMID: 23643712 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2013 Elsevier B.V. All rights reserved.

Chemical References

• Acyl Coenzyme A
• Carboxylic Acids
• Dicarboxylic Acids
• Esters
• methylmalonyl-coenzyme A
• isobutyryl-coenzyme A
• butyryl-coenzyme A
• glutaryl-coenzyme A
• propionyl-coenzyme A
• Glutamic Acid
• isovaleryl-coenzyme A
• succinyl-coenzyme A
• Amino-Acid N-Acetyltransferase

Topics

• Acyl Coenzyme A (metabolism, pharmacology)
• Amino-Acid N-Acetyltransferase (antagonists & inhibitors, metabolism)
• Carboxylic Acids (metabolism)
• Chromatography, High Pressure Liquid (methods)
• Dicarboxylic Acids (metabolism)
• Dose-Response Relationship, Drug
• Esters
• Glutamic Acid (chemistry, metabolism)
• Humans
• Hyperammonemia (metabolism)
• Kinetics
• Tandem Mass Spectrometry