[Enzymatic studies on human carcinoma tissues,--especially, study on beta-N-acetylhexosaminidases in oral and...

Activities of beta-hexosaminidase A and B were measured in both human lung and oral carcinomas. The specific activities of total beta-hexosaminidase were increased in both tissues, irrespective of histological types. In isoelectric focusing experiments, beta-hexosaminidase B from normal lung exhibited a single peak with an isoelectric point (pI) of 7.9, while beta-hexosaminidase B from adenocarcinoma contained two forms with pI of 7.6 and 7.9. With respect to heat stability, beta-hexosaminidase B from normal lung was very stable at 52 degrees, while tumor beta-hexosaminidase B was unstable. After treatment of the enzyme with dithiothreitol, the heat stability was restored. When the tumor pI 7.6 form was treated with dithiothreitol and subjected to polyacrylamide gel electrophoresis, the enzyme converted to pI 7.9 form, which was similar to that of the normal lung. Determination of the sulfhydryl group of the tumor pI 7.6 form under non-denaturing conditions showed that the enzyme did have some easily reducible disulfide bonds on its surface. These findings indicated that the formation of mixed disulfide bonds in the tumor beta-hexosaminidase B increased the net negative charge and resulted in the appearance of a heat-stable form.