Encyclopedia of Intensive Care Medicine

2012 Edition
| Editors: Jean-Louis Vincent, Jesse B. Hall

N-Acetyl-beta-D-Glucosaminidase (NAG)

  • Xiaoyan WenEmail author
  • John A. Kellum
Reference work entry
DOI: https://doi.org/10.1007/978-3-642-00418-6_305


N-Acetyl-/β-glucosaminidase (NAG) is a high molecular-weight (∼140 kDa) hydrolytic lysosomal enzyme that is found in many tissues of the body. It breaks chemical bonds of glycosides and amino sugars that form structural components in many tissues. It is necessary for the degradation and disposal of various parts of the cell, including the cell membrane.


NAG present in high concentration in the lysosomes of proximal renal tubular cells. There are two main isoenzymes found in human kidneys. Isoenzyme-A is part of intralysosomal compartment excreted in urine due to exocytosis. Isoenzyme-B is associated to the lysosomal membrane and excreted in urine during tubular damage. These two enzymes differ in their heat sensitivity and stable in acid urine [1]. Because of its stability in urine, its relatively large molecular mass which precludes filtration by the glomerulus and its presence in high activity in the tubular lysosomes, elevation of urinary NAG activity has...

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© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  1. 1.Department of Critical Care MedicineUniversity of Pittsburgh School of MedicinePittsburghUSA