Improved kinetic rate assay of urinary N-acetyl-beta-D-glucosaminidase with 2-chloro-4-nitrophenyl-N-acetyl-beta-D-glucosaminide as substrate.

We have improved the kinetic rate assay method for determining N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30; NAG) activity in urine with use of the synthetic substrate, 2-chloro-4-nitrophenyl-N-acetyl-beta-D-glucosaminide (CNP-NAG), reported previously (Clin Chem 1988;34:2140-2). To increase the solubility of this substrate, we used crown ether (15-crown-5-ether) and ethylene glycol. In addition, we used for the standard solution NAG from human placenta, with specificity corresponding to that of human urine, so that values obtained with the CNP-NAG method and a p-nitrophenyl-NAG method ("MEI Assay NAG") correlated almost completely (r = 0.995, n = 29). Reference values for urinary NAG activity determined by the CNP-NAG method were established for untimed urine specimens from 674 healthy volunteers. The normal reference interval (mean +/- 2 SD) for NAG: 1.6-15.0 (mean 4.9) U per gram of creatinine.