Stabilities of N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes in urine: advantage of NAG isoenzyme B measurement in clinical applications.
N-Acetyl-beta-D-glucosaminidase (NAG) is a widely used urinary enzyme for the assessment of renal diseases. We studied the stabilities of NAG isoenzymes in urine at 37 degrees C by enzyme assay and ELISA using a model simulating in vivo conditions. The stabilities were found to be affected by the pH. Under mild acidic condition (about pH 6), there was no significant loss of enzymatic activity of NAG isoenzyme A, enzymatic activity of NAG isoenzyme B and immunological activity of NAG isoenzyme B even after 8 h incubation. In contrast, under alkaline condition (about pH 8), the enzymatic activity of NAG isoenzyme A was rapidly lost, whereas both enzymatic and immunological activities of NAG isoenzyme B were maintained at more than 80% of their initial values. Also, we found that the ratios of endogenous NAG isoenzyme B to total NAG were elevated in alkaline urine samples. These results indicate that NAG isoenzyme A, which is a major isoenzyme in normal urine (pH 5-7), seems to be inactivated in alkaline urine. Our results suggest that for alkaline urine, NAG isoenzyme B should be measured to avoid misinterpretation of total NAG enzymatic activities.
Morita
A
A
Diagnostic Science Division, Shionogi & Co., Ltd., Osaka, Japan.
Numata
Y
Y
Kosugi
Y
Y
Noto
A
A
Takeuchi
N
N
Uchida
K
K
D000118:Acetylglucosaminidase / Q000652:urine*; D001424:Bacterial Infections / Q000201:enzymology / Q000652:urine; D004795:Enzyme Stability; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000652:urine*; D011704:Pyelonephritis / Q000201:enzymology / Q000652:urine
D007527:Isoenzymes; D000118:Acetylglucosaminidase