Assay of serum/plasma beta-N-acetylhexosaminidase isoenzymes by heat inactivation using a continuous spectrophotometric method adapted to a centrifugal analyzer.

Activity of serum/plasma beta-N-acetylhexosaminidase (EC 3.2.1.52) was determined by means of a continuous spectrophotometric method using 3,3'-dichlorophenylsulphonphthaleinyl-N-acetyl-beta-D-glucosaminid e as substrate, with very satisfactory results. Incubation of an undiluted aliquot (1 ml) of samples at 52 degrees C for 8 hours with an adjusted pH 5.5-6.0 provoked only the inactivation of isoenzyme A, thus allowing the evaluation of beta-N-acetylhexosaminidase isoenzyme composition. In 25 serum samples from control subjects and pregnant women, a good correlation between the percentage of isoenzyme B obtained by this procedure and the fluorimetric assay of O'Brien et al. (New Engl J Med 1970; 273:15-20) was found (r = 0.983, S(yx) = 1.51), with no statistically significant difference between the means (43.2 vs 42.8%). In 84 healthy adult subjects, an average value of 30.3% for the proportion of isoenzyme B was obtained, with an interval of 25.4-35.0%, in agreement with results reported by other authors.