Two Assays for Urinary N-Acetyl-β-d-glucosaminidase Compared

Abstract

In the course of investigating the exposure of gold miners and other workers to mercury, investigators at the National Institute for Occupational Safety & Health (NIOSH) measured urine N -acetyl-β-d-glucosaminidase (NAG; EC 3.2.1.52) activity to monitor for renal injury (1)(2)(3). Numerous methods are available for the urinalysis of NAG activity (4). Most of the analyses for the NIOSH studies were performed by Pacific Toxicology Laboratories, using the Kamiya Biomedical Company reagent set, which was based on NAG-catalyzed hydrolysis of 6-methyl-2-pyridyl- N -acetyl-1-thio-β-d-glucosaminide to 6-methyl-2-pyridinethiol. However, while planning our most recent investigational visit to a gold mine, we learned that the Kamiya Biomedical reagent set was temporarily out of stock. Consequently, we decided to perform the analyses in-house using the reagent set manufactured by Boehringer Mannheim Biochemica, which we had used previously for the determination of NAG in rats. This reagent set is based on NAG-catalyzed hydrolysis of the sodium salt of 3-cresolsulfonphthaleinyl- N -acetyl-β-d-glucosaminide to give 3-cresol purple (3-cresolsulfonphthalein, sodium salt). Because the two assays are based on the hydrolysis of different substrates, and in light of the differences reported among four NAG assays (including the 3-cresol purple) (5), we suspected that the 3-cresol purple assay might not give NAG activity results equivalent to those obtained by the 6-methyl-2-pyridinethiol assay used in …