N-acetyl-beta-hexosaminidase activity and isoenzymes in human gastric adenocarcinoma

The enhancement of lysosomal beta-hexosaminidase degradative activity in different human cancer tissues is fairly well documented. Gastric tumors have attracted considerable attention on the basis of their social incidence and clinical recurrence. Here we report a comparative study of beta-hexosaminidase activity and of its isoenzymes beta-hexosaminidase A (HA) and beta-hexosaminidase B (HB) from gastric adenocarcinoma and normal mucosa. Tumor beta-hexosaminidase activity from crude extracts and chromatographically resolved HA and HB forms were analyzed as regards their physicochemical and enzymatic properties and were compared to similar samples obtained from control tissue. The existence of one active site in the beta-hexosaminidase enzyme responsible for both N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D- galactosaminidase activities was determined. Apart from their relative contributions to beta-hexosaminidase activities, two major differences appeared in tumor HA and HB forms with respect to the corresponding controls: (1) the presence of an atypical heat-stable HB isoenzyme in gastric adenocarcinoma, and (2) a significantly increased Vmax of the HA form acting on both p-nitrophenyl-N-acetyl-beta-D-glucosaminide and p-nitrophenyl-N-acetyl-beta-D-galactosaminide substrates. The results show that the beta-hexosaminidase HA and HB isoenzymes from gastric adenocarcinoma display different patterns of response from the same forms from other human tumors.