[Determination of urinary NAG isozyme by thermal inactivation and the age difference]

We studied isozymes of urinary beta-D-N-acetylglucosaminidase (NAG), NAG-A and NAG-B, to develop a method for the determination of them. Urinary NAG-A was demonstrated to be measured most appropriately by the thermal inactivation at 50 degrees C for 4 hours in the buffer solution of pH 4.8. Using this method, 13 subjects were simultaneously measured for the levels of both urinary and serum NAG-A, which revealed no significant relation between them (r = 0.03). A significant increase in the mean value of urinary NAG-A activities (U/ml) was found in the 11-12 year-old subjects compared with those in the 6-7 year-old subjects. Although no significant differences were revealed among the total urinary NAG activities of the subjects, the values of NAG-A/total NAG (percent) tended to increase as the ages of the subjects increasing. In conclusion, when determining urinary NAG levels, a careful consideration must be taken into account for the presence of heterozygous carriers for Tay-Sachs disease who have a 50%-deficiency of NAG-A activity and for the age difference of the values.