Nit1 is a metabolite repair enzyme that hydrolyzes deaminated glutathione

Proc Natl Acad Sci U S A. 2017 Apr 18;114(16):E3233-E3242. doi: 10.1073/pnas.1613736114. Epub 2017 Apr 3.


The mammalian gene Nit1 (nitrilase-like protein 1) encodes a protein that is highly conserved in eukaryotes and is thought to act as a tumor suppressor. Despite being ∼35% sequence identical to ω-amidase (Nit2), the Nit1 protein does not hydrolyze efficiently α-ketoglutaramate (a known physiological substrate of Nit2), and its actual enzymatic function has so far remained a puzzle. In the present study, we demonstrate that both the mammalian Nit1 and its yeast ortholog are amidases highly active toward deaminated glutathione (dGSH; i.e., a form of glutathione in which the free amino group has been replaced by a carbonyl group). We further show that Nit1-KO mutants of both human and yeast cells accumulate dGSH and the same compound is excreted in large amounts in the urine of Nit1-KO mice. Finally, we show that several mammalian aminotransferases (transaminases), both cytosolic and mitochondrial, can form dGSH via a common (if slow) side-reaction and provide indirect evidence that transaminases are mainly responsible for dGSH formation in cultured mammalian cells. Altogether, these findings delineate a typical instance of metabolite repair, whereby the promiscuous activity of some abundant enzymes of primary metabolism leads to the formation of a useless and potentially harmful compound, which needs a suitable "repair enzyme" to be destroyed or reconverted into a useful metabolite. The need for a dGSH repair reaction does not appear to be limited to eukaryotes: We demonstrate that Nit1 homologs acting as excellent dGSH amidases also occur in Escherichia coli and other glutathione-producing bacteria.

Keywords: amidase; aminotransferases; deaminated glutathione; metabolite repair.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminohydrolases / metabolism*
  • Aminohydrolases / physiology
  • Animals
  • Deamination
  • Glutathione / metabolism*
  • Humans
  • Hydrolysis
  • Mice
  • Mice, Knockout
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Substrate Specificity
  • Transaminases / metabolism*


  • Saccharomyces cerevisiae Proteins
  • Transaminases
  • Aminohydrolases
  • nitrilase
  • Glutathione