Impaired ureagenesis due to arginine-insensitive N-acetylglutamate synthase

Parthasarathy Sonaimuthu, Emilee Senkevitch, Nantaporn Haskins, Prech Uapinyoying, Markey McNutt, Hiroki Morizono, Mendel Tuchman, Ljubica Caldovic

Research output: Contribution to journalArticlepeer-review

Abstract

The urea cycle protects the central nervous system from ammonia toxicity by converting ammonia to non-toxic urea. N-acetylglutamate synthase (NAGS) is an enzyme that catalyzes the formation of N-acetylglutamate (NAG), an allosteric activator of carbamylphosphate synthetase 1 (CPS1), the rate limiting enzyme of the urea cycle. Enzymatic activity of mammalian NAGS doubles in the presence of L-arginine but the physiological significance of NAGS activation by L-arginine is unknown. Previously, we have described the creation of a NAGS knockout (Nags−/−) mouse, which develops hyperammonemia without N-carbamylglutamate and L-citrulline supplementation (NCG+Cit). In order to investigate the effect of L-arginine on ureagenesis in vivo, we used adeno associated virus (AAV) mediated gene transfer to deliver either wild-type or E354A mutant mouse NAGS (mNAGS), which is not activated by L-arginine, to Nags−/− mice. The ability of the E354A mNAGS mutant protein to rescue Nags−/− mice was determined by measuring their activity on the voluntary wheel following NCG+Cit withdrawal. The Nags−/− mice that received E354A mNAGS remained apparently healthy and active but had elevated plasma ammonia concentration despite similar expression levels of the E354A mNAGS and control wild-type NAGS proteins. The corresponding mutation in human NAGS (NP 694551.1:p.E360D) that abolishes binding and activation by L-arginine was also identified in a patient with hyperammonemia due to NAGS deficiency. Taken together, our results suggest that L-arginine binding to the NAGS enzyme is essential for normal ureagenesis.

Original languageEnglish (US)
JournalUnknown Journal
DOIs
StatePublished - Sep 25 2018

Keywords

  • arginine
  • N-acetylglutamate
  • N-acetylglutamate synthase
  • regulation
  • urea cycle
  • ureagenesis

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)
  • Immunology and Microbiology(all)
  • Neuroscience(all)
  • Pharmacology, Toxicology and Pharmaceutics(all)

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