Biochemical characterization of liver microsomal, Golgi, lysosomal, and serum beta-glucuronidases in dibutyl...

Organophosphate compounds are known to cause the selective release of rat liver microsomal beta-glucuronidase into plasma. To investigate the alterations of molecular forms and oligosaccharide moieties of liver beta-glucuronidase in organophosphate compound-administered rats, beta-glucuronidase was isolated from microsomal, Golgi, lysosomal, and serum fractions. In SDS-polyacrylamide gel electrophoresis, a single polypeptide band was observed on gels in Golgi and serum beta-glucuronidases. This result indicated that Golgi and serum beta-glucuronidases of treated rats did not undergo post-translational proteolytic processing, in contrast to those in control rat livers. Biochemical characterization of the isolated beta-glucuronidases by employing lectin affinity chromatography revealed that interaction of serum and Golgi enzymes with Ricinus communis agglutinin- and wheat germ agglutinin-Sepharose was fairly strong, and that microsomal and lysosomal enzymes were poorly retained on those columns. These results suggested that the serum and Golgi beta-glucuronidases are sialoglycoproteins. A clearance study also showed that infused serum beta-glucuronidase was slowly cleared from plasma with a half-life of about 60 min, but the asialo-serum enzyme was rapidly cleared with a half-life of about 5 min. These results imply that microsomal beta-glucuronidase undergoes extensive modification of the oligosaccharide moieties by terminal glycosyltransferases at the trans Golgi when it is destined for secretion into serum in response to treatment with an organophosphate compound.