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

The enhancement of lysosomal beta-hexosaminidase degradative activity in di fferent human cancer tissues is fairly well documented. Gastric tumors have attracted considerable attention on the basis of their social incidence an d clinical recurrence. Here we report a comparative study of beta-hexosamin idase activity and of its isoenzymes beta-hexosaminidase A (HA) and beta-he xosaminidase B (HB) from gastric adenocarcinoma and normal mucosa. Tumor be ta-hexosaminidase activity from crude extracts and chromatographically reso lved HA and HE forms were analyzed as regards their physicochemical and enz ymatic properties and were compared to similar samples obtained from contro l tissue. The existence of one active site in the beta-hexosaminidase enzym e responsible for both N-acetyl-beta-D-glucosaminidase and N-acetyl-beta-D- galactosaminidase activities was determined. Apart from their relative cont ributions to beta-hexosaminidase activities, two major differences appeared in tumor HA and HE forms with respect to the corresponding controls: (1) t he presence of an atypical heat-stable HB isoenzyme in gastric adenocarcino ma, and (2) a significantly increased V-max 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 HE isoenzymes from gastric adenocarcinoma display different pattern s of response from the same forms from other human tumors.