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

Nit1 is a metabolite repair enzyme that hydrolyzes deaminated glutathione.

Author information

Walloon Excellence in Lifesciences and Biotechnology, B-1200 Brussels, Belgium;
de Duve Institute, Université Catholique de Louvain, B-1200 Brussels, Belgium.
Department of Life Sciences, Laboratory of Biochemistry, Molecular Biology, and Bioinformatics, University of Parma, 43124 Parma, Italy.
Japan Clinical Metabolomics Institute, Kahoku, Ishikawa 929-1174, Japan.
Human Genetics, Medical Research Institute, Kanazawa Medical University, Uchinada, Ishikawa 920-0293, Japan.
Luxembourg Centre for Systems Biomedicine, Université du Luxembourg, L-4367 Belvaux, Luxembourg.
Ludwig Institute for Cancer Research, de Duve Institute, Université Catholique de Louvain, B-1200 Brussels, Belgium.
Walloon Excellence in Lifesciences and Biotechnology, B-1200 Brussels, Belgium.
Department of Cancer Biology and Genetics, Ohio State University, Columbus, OH 43210.
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595.


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highly active toward deaminated glutathione (dGSH; i.e., a form of glutathione in which the free amino group has been replaced by a carbonyl group).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.


amidase; aminotransferases; deaminated glutathione; metabolite repair

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