Occurrence and subcellular distribution of the NADPHX repair system in mammals

Biochem J. 2014 May 15;460(1):49-58. doi: 10.1042/BJ20131482.


Hydration of NAD(P)H to NAD(P)HX, which inhibits several dehydrogenases, is corrected by an ATP-dependent dehydratase and an epimerase recently identified as the products of the vertebrate Carkd (carbohydrate kinase domain) and Aibp (apolipoprotein AI-binding protein) genes respectively. The purpose of the present study was to assess the presence of these enzymes in mammalian tissues and determine their subcellular localization. The Carkd gene encodes proteins with a predicted mitochondrial propeptide (mCARKD), a signal peptide (spCARKD) or neither of them (cCARKD). Confocal microscopy analysis of transfected CHO (Chinese-hamster ovary) cells indicated that cCARKD remains in the cytosol, whereas mCARKD and spCARKD are targeted to the mitochondria and the endoplasmic reticulum respectively. Unlike the other two forms, spCARKD is N-glycosylated, supporting its targeting to the endoplasmic reticulum. The Aibp gene encodes two different proteins, which we show to be targeted to the mitochondria (mAIBP) and the cytosol (cAIBP). Quantification of the NAD(P)HX dehydratase and epimerase activities in rat tissues, performed after partial purification, indicated that both enzymes are widely distributed, with total activities of ≈3-10 nmol/min per g of tissue. Liver fractionation by differential centrifugation confirmed the presence of the dehydratase and the epimerase in the cytosol and in mitochondria. These data support the notion that NAD(P)HX repair is extremely widespread.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alternative Splicing / genetics
  • Amino Acid Sequence
  • Animals
  • CHO Cells
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cricetinae
  • Cricetulus
  • Cytosol / enzymology*
  • DNA Repair / genetics*
  • DNA-Binding Proteins
  • Endoplasmic Reticulum / enzymology
  • Endoplasmic Reticulum / genetics
  • HEK293 Cells
  • Humans
  • Mice
  • Mitochondria / enzymology*
  • Mitochondria / genetics
  • Molecular Sequence Data
  • NADP / genetics
  • NADP / metabolism*
  • Phosphoproteins / genetics
  • Phosphoproteins / metabolism*
  • Phosphotransferases (Alcohol Group Acceptor) / chemistry
  • Phosphotransferases (Alcohol Group Acceptor) / genetics*
  • Racemases and Epimerases
  • Rats
  • Subcellular Fractions / enzymology
  • Tissue Distribution / genetics
  • Transcription Factors / chemistry
  • Transcription Factors / genetics*


  • AUNIP protein, human
  • Carrier Proteins
  • DNA-Binding Proteins
  • Phosphoproteins
  • Transcription Factors
  • NADP
  • Phosphotransferases (Alcohol Group Acceptor)
  • Naxd protein, rat
  • SHPK protein, human
  • Naxe protein, mouse
  • Racemases and Epimerases